diff --git a/README.md b/README.md
index b68c384..8fa0973 100644
--- a/README.md
+++ b/README.md
@@ -138,25 +138,21 @@ most complex.
     (drag it by its title bar, Close button, window focus, multiple overlapping
     windows, and so on).
 * [x] **Tooltip**: a mouse hover label attached to a widget.
+* [x] **MenuButton**: a button that opens a modal pop-up menu on click.
+* [x] **MenuBar**: a specialized Frame that groups a bunch of MenuButtons and
+  provides a simple API to add menus and items to it.
+* [x] **Menu**: a frame full of clickable links and separators. Usually used as
+  a modal pop-up by the MenuButton and MenuBar.
 
 **Work in progress widgets:**
 
-* [x] **Menu**: a frame with clickable menu items.
-  * To be a base widget behind right-click context menus, pull-down menus
-    from a MenuBar, options from a SelectBox and so on.
-  * Powered by Frame and Button but with a nice API for composing menu
-    actions.
-  * Partially implemented so far.
-* [ ] **MenuButton**: a Button that opens a Menu when clicked.
-* [ ] **MenuBar**: a Frame that houses many MenuButtons, intended for the
-  main menu at the top of a UI window (File, Edit, Help, etc.).
 * [ ] **Scrollbar**: a Frame including a trough, scroll buttons and a
   draggable slider.
+* [ ] **SelectBox:** a kind of MenuButton that lets the user choose a value
+  from a list of possible values, bound to a string variable.
 
 **Wish list for the longer-term future:**
 
-* [ ] **SelectBox:** a kind of MenuButton that lets the user choose a value
-  from a list of possible values, bound to a string variable.
 * [ ] **TextBox:** an editable text field that the user can focus and type
   a value into.
   * Would depend on the WindowManager to manage focus for the widgets.
diff --git a/debug.go b/debug.go
index 4ce10d0..f25d42b 100644
--- a/debug.go
+++ b/debug.go
@@ -5,6 +5,14 @@ import (
 	"strings"
 )
 
+// PrintWidgetTree prints a widget tree to console.
+func PrintWidgetTree(root Widget) {
+	fmt.Printf("--- Widget Tree of %s ---\n", root)
+	for _, row := range WidgetTree(root) {
+		fmt.Println(row)
+	}
+}
+
 // WidgetTree returns a string representing the tree of widgets starting
 // at a given widget.
 func WidgetTree(root Widget) []string {
diff --git a/docs/menus-1.png b/docs/menus-1.png
new file mode 100644
index 0000000..3f3973f
Binary files /dev/null and b/docs/menus-1.png differ
diff --git a/docs/menus-2.png b/docs/menus-2.png
new file mode 100644
index 0000000..5f9c7e0
Binary files /dev/null and b/docs/menus-2.png differ
diff --git a/eg/README.md b/eg/README.md
new file mode 100644
index 0000000..5ab58e6
--- /dev/null
+++ b/eg/README.md
@@ -0,0 +1,10 @@
+# Examples for go/ui
+
+* [Hello, World!](hello-world/): a basic UI demo.
+* [Frame Place()](frame-place/): demonstrates using the Place() layout management
+  option for Frame widgets.]
+* [Window Manager](windows/): demonstrates the Window widget and window
+  management features of the Supervisor.
+* [Tooltip](tooltip/): demonstrates the Tooltip widget on a variety of buttons
+  scattered around the window.
+* [Menus](menus/): demonstrates various Menu Buttons and a Menu Bar.
diff --git a/eg/menus/Makefile b/eg/menus/Makefile
new file mode 100644
index 0000000..b5b7bbb
--- /dev/null
+++ b/eg/menus/Makefile
@@ -0,0 +1,11 @@
+.PHONY: run
+run:
+	go run main.go
+
+.PHONY: wasm
+wasm:
+	GOOS=js GOARCH=wasm go build -v -o windows.wasm main_wasm.go
+
+.PHONY: wasm-serve
+wasm-serve: wasm
+	../wasm-common/serve.sh
diff --git a/eg/menus/README.md b/eg/menus/README.md
new file mode 100644
index 0000000..d80001f
--- /dev/null
+++ b/eg/menus/README.md
@@ -0,0 +1,19 @@
+# Menu Example
+
+This example shows off the Menu, MenuButton, and MenuBar widgets.
+
+* MenuButton is your basic button that pops up a Menu when clicked.
+* MenuBar is a specialized Frame that attaches to the top of the parent
+  (usually the window) and provides a simple API to add menus and items.
+* Menu is the underlying "pop-up and select an item" widget.
+
+## Running It
+
+From your terminal, just type `go run main.go` or `make run` from this
+example's directory.
+
+## Screenshots
+
+![Screenshot 1](../../docs/menus-1.png)
+
+![Screenshot 2](../../docs/menus-2.png)
diff --git a/eg/menus/main.go b/eg/menus/main.go
new file mode 100644
index 0000000..254634f
--- /dev/null
+++ b/eg/menus/main.go
@@ -0,0 +1,208 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"git.kirsle.net/go/render"
+	"git.kirsle.net/go/render/event"
+	"git.kirsle.net/go/render/sdl"
+	"git.kirsle.net/go/ui"
+)
+
+// Program globals.
+var (
+	// Size of the MainWindow.
+	Width  = 640
+	Height = 480
+
+	BGColor = render.White
+)
+
+func init() {
+	sdl.DefaultFontFilename = "../DejaVuSans.ttf"
+}
+
+func main() {
+	mw, err := ui.NewMainWindow("Menu Demo", Width, Height)
+	if err != nil {
+		panic(err)
+	}
+
+	setupMainMenu(mw)
+
+	// Menu button in middle of window.
+	{
+		btn := ui.NewMenuButton("MenuBtn", ui.NewLabel(ui.Label{
+			Text: "Click me!",
+		}))
+		btn.Supervise(mw.Supervisor())
+		mw.Place(btn, ui.Place{
+			Center: true,
+			Middle: true,
+		})
+
+		for _, label := range []string{
+			"MenuButtons open menus",
+			"when clicked. MenuBar is ",
+			"a Frame of MenuButtons",
+			"attached to the top of the",
+			"window.",
+			"",
+			"They all provide a nice API",
+			"to insert menus and items.",
+		} {
+			label := label
+			if label == "" {
+				btn.AddSeparator()
+				continue
+			}
+			btn.AddItem(label, func() {
+				fmt.Printf("Button '%s' clicked!\n", label)
+			})
+		}
+
+	}
+
+	// Menu button on the bottom right of screen.
+	{
+		btn := ui.NewMenuButton("BrBtn", ui.NewLabel(ui.Label{
+			Text: "Fruits",
+		}))
+		btn.Supervise(mw.Supervisor())
+		mw.Place(btn, ui.Place{
+			Right:  20,
+			Bottom: 20,
+		})
+
+		btn.AddItem("Apples", func() {})
+		btn.AddItem("Oranges", func() {})
+		btn.AddItem("Bananas", func() {})
+		btn.AddItem("Pears", func() {})
+	}
+
+	// Menu button on the bottom left of screen.
+	{
+		btn := ui.NewMenuButton("BlBtn", ui.NewLabel(ui.Label{
+			Text: "Set Window Color",
+		}))
+		btn.Supervise(mw.Supervisor())
+		mw.Place(btn, ui.Place{
+			Left:   20,
+			Bottom: 20,
+		})
+
+		setBg := func(color render.Color) func() {
+			return func() {
+				BGColor = color
+			}
+		}
+
+		// Really fancy buttons.
+		var colors = []struct {
+			label string
+			hex   string
+			color render.Color
+		}{
+			{"Black", "#000", render.Black},
+			{"Red", "#F00", render.Red},
+			{"Yellow", "#FF0", render.Yellow},
+			{"Green", "#0F0", render.Green},
+			{"Cyan", "#0FF", render.Cyan},
+			{"Blue", "#00F", render.Blue},
+			{"Magenta", "#F0F", render.Magenta},
+			{"White", "#FFF", render.White},
+		}
+		for _, opt := range colors {
+			item := btn.AddItemAccel(opt.label, opt.hex, setBg(opt.color))
+			item.SetBackground(opt.color.Lighten(128))
+		}
+
+		// btn.AddItemAccel("Black", "#000", setBg(render.White))
+		// btn.AddItemAccel("Red", "#F00", setBg(render.Red))
+		// btn.AddItemAccel("Yellow", "#FF0", setBg(render.Yellow))
+		// btn.AddItemAccel("Green", "#0F0", setBg(render.Green))
+		// btn.AddItemAccel("Cyan", "#0FF", setBg(render.Cyan))
+		// btn.AddItemAccel("Blue", "#00F", setBg(render.Blue))
+		// btn.AddItemAccel("Magenta", "#F0F", setBg(render.Magenta))
+		// btn.AddItemAccel("White", "#FFF", setBg(render.White))
+	}
+
+	// The "Long Menu" on the middle left side
+	{
+		btn := ui.NewMenuButton("BlBtn", ui.NewLabel(ui.Label{
+			Text: "Tall Growing Menu",
+		}))
+		btn.Supervise(mw.Supervisor())
+		mw.Place(btn, ui.Place{
+			Left:   20,
+			Middle: true,
+		})
+
+		var id int
+		btn.AddItem("Add New Option", func() {
+			id++
+			id := id
+			btn.AddItem(fmt.Sprintf("Menu Item #%d", id), func() {
+				fmt.Printf("Chosen menu item %d\n", id)
+			})
+		})
+
+		btn.AddSeparator()
+	}
+
+	mw.OnLoop(func(e *event.State) {
+		mw.SetBackground(BGColor)
+		if e.Up {
+			fmt.Println("Supervised widgets:")
+			for widg := range mw.Supervisor().Widgets() {
+				fmt.Printf("%+v\n", widg)
+			}
+		}
+		if e.Escape {
+			os.Exit(0)
+		}
+	})
+
+	mw.MainLoop()
+}
+
+func setupMainMenu(mw *ui.MainWindow) {
+	bar := ui.NewMenuBar("Main Menu")
+
+	fileMenu := bar.AddMenu("File")
+	fileMenu.AddItemAccel("New", "Ctrl-N", func() {
+		fmt.Println("Chose File->New")
+	})
+	fileMenu.AddItemAccel("Open", "Ctrl-O", func() {
+		fmt.Println("Chose File->Open")
+	})
+	fileMenu.AddSeparator()
+	fileMenu.AddItemAccel("Exit", "Alt-F4", func() {
+		fmt.Println("Chose File->Exit")
+		os.Exit(0)
+	})
+
+	editMenu := bar.AddMenu("Edit")
+	editMenu.AddItemAccel("Undo", "Ctrl-Z", func() {})
+	editMenu.AddItemAccel("Redo", "Shift-Ctrl-Z", func() {})
+	editMenu.AddSeparator()
+	editMenu.AddItemAccel("Cut", "Ctrl-X", func() {})
+	editMenu.AddItemAccel("Copy", "Ctrl-C", func() {})
+	editMenu.AddItemAccel("Paste", "Ctrl-V", func() {})
+	editMenu.AddSeparator()
+	editMenu.AddItem("Settings...", func() {})
+
+	viewMenu := bar.AddMenu("View")
+	viewMenu.AddItemAccel("Toggle Full Screen", "F11", func() {})
+
+	helpMenu := bar.AddMenu("Help")
+	helpMenu.AddItemAccel("Contents", "F1", func() {})
+	helpMenu.AddItem("About", func() {})
+
+	bar.Supervise(mw.Supervisor())
+	bar.Compute(mw.Engine)
+	mw.Pack(bar, bar.PackTop())
+
+	fmt.Printf("Setup MenuBar: %s\n", bar.Size())
+}
diff --git a/eg/wasm-common/wasm_exec.js b/eg/wasm-common/wasm_exec.js
index a54bb9a..bb66cf2 100644
--- a/eg/wasm-common/wasm_exec.js
+++ b/eg/wasm-common/wasm_exec.js
@@ -30,6 +30,12 @@
 		global.fs = require("fs");
 	}
 
+	const enosys = () => {
+		const err = new Error("not implemented");
+		err.code = "ENOSYS";
+		return err;
+	};
+
 	if (!global.fs) {
 		let outputBuf = "";
 		global.fs = {
@@ -45,27 +51,53 @@
 			},
 			write(fd, buf, offset, length, position, callback) {
 				if (offset !== 0 || length !== buf.length || position !== null) {
-					throw new Error("not implemented");
+					callback(enosys());
+					return;
 				}
 				const n = this.writeSync(fd, buf);
 				callback(null, n);
 			},
-			open(path, flags, mode, callback) {
-				const err = new Error("not implemented");
-				err.code = "ENOSYS";
-				callback(err);
-			},
-			read(fd, buffer, offset, length, position, callback) {
-				const err = new Error("not implemented");
-				err.code = "ENOSYS";
-				callback(err);
-			},
-			fsync(fd, callback) {
-				callback(null);
-			},
+			chmod(path, mode, callback) { callback(enosys()); },
+			chown(path, uid, gid, callback) { callback(enosys()); },
+			close(fd, callback) { callback(enosys()); },
+			fchmod(fd, mode, callback) { callback(enosys()); },
+			fchown(fd, uid, gid, callback) { callback(enosys()); },
+			fstat(fd, callback) { callback(enosys()); },
+			fsync(fd, callback) { callback(null); },
+			ftruncate(fd, length, callback) { callback(enosys()); },
+			lchown(path, uid, gid, callback) { callback(enosys()); },
+			link(path, link, callback) { callback(enosys()); },
+			lstat(path, callback) { callback(enosys()); },
+			mkdir(path, perm, callback) { callback(enosys()); },
+			open(path, flags, mode, callback) { callback(enosys()); },
+			read(fd, buffer, offset, length, position, callback) { callback(enosys()); },
+			readdir(path, callback) { callback(enosys()); },
+			readlink(path, callback) { callback(enosys()); },
+			rename(from, to, callback) { callback(enosys()); },
+			rmdir(path, callback) { callback(enosys()); },
+			stat(path, callback) { callback(enosys()); },
+			symlink(path, link, callback) { callback(enosys()); },
+			truncate(path, length, callback) { callback(enosys()); },
+			unlink(path, callback) { callback(enosys()); },
+			utimes(path, atime, mtime, callback) { callback(enosys()); },
 		};
 	}
 
+	if (!global.process) {
+		global.process = {
+			getuid() { return -1; },
+			getgid() { return -1; },
+			geteuid() { return -1; },
+			getegid() { return -1; },
+			getgroups() { throw enosys(); },
+			pid: -1,
+			ppid: -1,
+			umask() { throw enosys(); },
+			cwd() { throw enosys(); },
+			chdir() { throw enosys(); },
+		}
+	}
+
 	if (!global.crypto) {
 		const nodeCrypto = require("crypto");
 		global.crypto = {
@@ -113,24 +145,19 @@
 			this._scheduledTimeouts = new Map();
 			this._nextCallbackTimeoutID = 1;
 
-			const mem = () => {
-				// The buffer may change when requesting more memory.
-				return new DataView(this._inst.exports.mem.buffer);
-			}
-
 			const setInt64 = (addr, v) => {
-				mem().setUint32(addr + 0, v, true);
-				mem().setUint32(addr + 4, Math.floor(v / 4294967296), true);
+				this.mem.setUint32(addr + 0, v, true);
+				this.mem.setUint32(addr + 4, Math.floor(v / 4294967296), true);
 			}
 
 			const getInt64 = (addr) => {
-				const low = mem().getUint32(addr + 0, true);
-				const high = mem().getInt32(addr + 4, true);
+				const low = this.mem.getUint32(addr + 0, true);
+				const high = this.mem.getInt32(addr + 4, true);
 				return low + high * 4294967296;
 			}
 
 			const loadValue = (addr) => {
-				const f = mem().getFloat64(addr, true);
+				const f = this.mem.getFloat64(addr, true);
 				if (f === 0) {
 					return undefined;
 				}
@@ -138,7 +165,7 @@
 					return f;
 				}
 
-				const id = mem().getUint32(addr, true);
+				const id = this.mem.getUint32(addr, true);
 				return this._values[id];
 			}
 
@@ -147,57 +174,62 @@
 
 				if (typeof v === "number") {
 					if (isNaN(v)) {
-						mem().setUint32(addr + 4, nanHead, true);
-						mem().setUint32(addr, 0, true);
+						this.mem.setUint32(addr + 4, nanHead, true);
+						this.mem.setUint32(addr, 0, true);
 						return;
 					}
 					if (v === 0) {
-						mem().setUint32(addr + 4, nanHead, true);
-						mem().setUint32(addr, 1, true);
+						this.mem.setUint32(addr + 4, nanHead, true);
+						this.mem.setUint32(addr, 1, true);
 						return;
 					}
-					mem().setFloat64(addr, v, true);
+					this.mem.setFloat64(addr, v, true);
 					return;
 				}
 
 				switch (v) {
 					case undefined:
-						mem().setFloat64(addr, 0, true);
+						this.mem.setFloat64(addr, 0, true);
 						return;
 					case null:
-						mem().setUint32(addr + 4, nanHead, true);
-						mem().setUint32(addr, 2, true);
+						this.mem.setUint32(addr + 4, nanHead, true);
+						this.mem.setUint32(addr, 2, true);
 						return;
 					case true:
-						mem().setUint32(addr + 4, nanHead, true);
-						mem().setUint32(addr, 3, true);
+						this.mem.setUint32(addr + 4, nanHead, true);
+						this.mem.setUint32(addr, 3, true);
 						return;
 					case false:
-						mem().setUint32(addr + 4, nanHead, true);
-						mem().setUint32(addr, 4, true);
+						this.mem.setUint32(addr + 4, nanHead, true);
+						this.mem.setUint32(addr, 4, true);
 						return;
 				}
 
-				let ref = this._refs.get(v);
-				if (ref === undefined) {
-					ref = this._values.length;
-					this._values.push(v);
-					this._refs.set(v, ref);
+				let id = this._ids.get(v);
+				if (id === undefined) {
+					id = this._idPool.pop();
+					if (id === undefined) {
+						id = this._values.length;
+					}
+					this._values[id] = v;
+					this._goRefCounts[id] = 0;
+					this._ids.set(v, id);
 				}
-				let typeFlag = 0;
+				this._goRefCounts[id]++;
+				let typeFlag = 1;
 				switch (typeof v) {
 					case "string":
-						typeFlag = 1;
-						break;
-					case "symbol":
 						typeFlag = 2;
 						break;
-					case "function":
+					case "symbol":
 						typeFlag = 3;
 						break;
+					case "function":
+						typeFlag = 4;
+						break;
 				}
-				mem().setUint32(addr + 4, nanHead | typeFlag, true);
-				mem().setUint32(addr, ref, true);
+				this.mem.setUint32(addr + 4, nanHead | typeFlag, true);
+				this.mem.setUint32(addr, id, true);
 			}
 
 			const loadSlice = (addr) => {
@@ -232,11 +264,13 @@
 
 					// func wasmExit(code int32)
 					"runtime.wasmExit": (sp) => {
-						const code = mem().getInt32(sp + 8, true);
+						const code = this.mem.getInt32(sp + 8, true);
 						this.exited = true;
 						delete this._inst;
 						delete this._values;
-						delete this._refs;
+						delete this._goRefCounts;
+						delete this._ids;
+						delete this._idPool;
 						this.exit(code);
 					},
 
@@ -244,20 +278,25 @@
 					"runtime.wasmWrite": (sp) => {
 						const fd = getInt64(sp + 8);
 						const p = getInt64(sp + 16);
-						const n = mem().getInt32(sp + 24, true);
+						const n = this.mem.getInt32(sp + 24, true);
 						fs.writeSync(fd, new Uint8Array(this._inst.exports.mem.buffer, p, n));
 					},
 
-					// func nanotime() int64
-					"runtime.nanotime": (sp) => {
+					// func resetMemoryDataView()
+					"runtime.resetMemoryDataView": (sp) => {
+						this.mem = new DataView(this._inst.exports.mem.buffer);
+					},
+
+					// func nanotime1() int64
+					"runtime.nanotime1": (sp) => {
 						setInt64(sp + 8, (timeOrigin + performance.now()) * 1000000);
 					},
 
-					// func walltime() (sec int64, nsec int32)
-					"runtime.walltime": (sp) => {
+					// func walltime1() (sec int64, nsec int32)
+					"runtime.walltime1": (sp) => {
 						const msec = (new Date).getTime();
 						setInt64(sp + 8, msec / 1000);
-						mem().setInt32(sp + 16, (msec % 1000) * 1000000, true);
+						this.mem.setInt32(sp + 16, (msec % 1000) * 1000000, true);
 					},
 
 					// func scheduleTimeoutEvent(delay int64) int32
@@ -276,12 +315,12 @@
 							},
 							getInt64(sp + 8) + 1, // setTimeout has been seen to fire up to 1 millisecond early
 						));
-						mem().setInt32(sp + 16, id, true);
+						this.mem.setInt32(sp + 16, id, true);
 					},
 
 					// func clearTimeoutEvent(id int32)
 					"runtime.clearTimeoutEvent": (sp) => {
-						const id = mem().getInt32(sp + 8, true);
+						const id = this.mem.getInt32(sp + 8, true);
 						clearTimeout(this._scheduledTimeouts.get(id));
 						this._scheduledTimeouts.delete(id);
 					},
@@ -291,6 +330,18 @@
 						crypto.getRandomValues(loadSlice(sp + 8));
 					},
 
+					// func finalizeRef(v ref)
+					"syscall/js.finalizeRef": (sp) => {
+						const id = this.mem.getUint32(sp + 8, true);
+						this._goRefCounts[id]--;
+						if (this._goRefCounts[id] === 0) {
+							const v = this._values[id];
+							this._values[id] = null;
+							this._ids.delete(v);
+							this._idPool.push(id);
+						}
+					},
+
 					// func stringVal(value string) ref
 					"syscall/js.stringVal": (sp) => {
 						storeValue(sp + 24, loadString(sp + 8));
@@ -308,6 +359,11 @@
 						Reflect.set(loadValue(sp + 8), loadString(sp + 16), loadValue(sp + 32));
 					},
 
+					// func valueDelete(v ref, p string)
+					"syscall/js.valueDelete": (sp) => {
+						Reflect.deleteProperty(loadValue(sp + 8), loadString(sp + 16));
+					},
+
 					// func valueIndex(v ref, i int) ref
 					"syscall/js.valueIndex": (sp) => {
 						storeValue(sp + 24, Reflect.get(loadValue(sp + 8), getInt64(sp + 16)));
@@ -327,10 +383,10 @@
 							const result = Reflect.apply(m, v, args);
 							sp = this._inst.exports.getsp(); // see comment above
 							storeValue(sp + 56, result);
-							mem().setUint8(sp + 64, 1);
+							this.mem.setUint8(sp + 64, 1);
 						} catch (err) {
 							storeValue(sp + 56, err);
-							mem().setUint8(sp + 64, 0);
+							this.mem.setUint8(sp + 64, 0);
 						}
 					},
 
@@ -342,10 +398,10 @@
 							const result = Reflect.apply(v, undefined, args);
 							sp = this._inst.exports.getsp(); // see comment above
 							storeValue(sp + 40, result);
-							mem().setUint8(sp + 48, 1);
+							this.mem.setUint8(sp + 48, 1);
 						} catch (err) {
 							storeValue(sp + 40, err);
-							mem().setUint8(sp + 48, 0);
+							this.mem.setUint8(sp + 48, 0);
 						}
 					},
 
@@ -357,10 +413,10 @@
 							const result = Reflect.construct(v, args);
 							sp = this._inst.exports.getsp(); // see comment above
 							storeValue(sp + 40, result);
-							mem().setUint8(sp + 48, 1);
+							this.mem.setUint8(sp + 48, 1);
 						} catch (err) {
 							storeValue(sp + 40, err);
-							mem().setUint8(sp + 48, 0);
+							this.mem.setUint8(sp + 48, 0);
 						}
 					},
 
@@ -384,7 +440,7 @@
 
 					// func valueInstanceOf(v ref, t ref) bool
 					"syscall/js.valueInstanceOf": (sp) => {
-						mem().setUint8(sp + 24, loadValue(sp + 8) instanceof loadValue(sp + 16));
+						this.mem.setUint8(sp + 24, loadValue(sp + 8) instanceof loadValue(sp + 16));
 					},
 
 					// func copyBytesToGo(dst []byte, src ref) (int, bool)
@@ -392,13 +448,13 @@
 						const dst = loadSlice(sp + 8);
 						const src = loadValue(sp + 32);
 						if (!(src instanceof Uint8Array)) {
-							mem().setUint8(sp + 48, 0);
+							this.mem.setUint8(sp + 48, 0);
 							return;
 						}
 						const toCopy = src.subarray(0, dst.length);
 						dst.set(toCopy);
 						setInt64(sp + 40, toCopy.length);
-						mem().setUint8(sp + 48, 1);
+						this.mem.setUint8(sp + 48, 1);
 					},
 
 					// func copyBytesToJS(dst ref, src []byte) (int, bool)
@@ -406,13 +462,13 @@
 						const dst = loadValue(sp + 8);
 						const src = loadSlice(sp + 16);
 						if (!(dst instanceof Uint8Array)) {
-							mem().setUint8(sp + 48, 0);
+							this.mem.setUint8(sp + 48, 0);
 							return;
 						}
 						const toCopy = src.subarray(0, dst.length);
 						dst.set(toCopy);
 						setInt64(sp + 40, toCopy.length);
-						mem().setUint8(sp + 48, 1);
+						this.mem.setUint8(sp + 48, 1);
 					},
 
 					"debug": (value) => {
@@ -424,7 +480,8 @@
 
 		async run(instance) {
 			this._inst = instance;
-			this._values = [ // TODO: garbage collection
+			this.mem = new DataView(this._inst.exports.mem.buffer);
+			this._values = [ // JS values that Go currently has references to, indexed by reference id
 				NaN,
 				0,
 				null,
@@ -433,10 +490,10 @@
 				global,
 				this,
 			];
-			this._refs = new Map();
-			this.exited = false;
-
-			const mem = new DataView(this._inst.exports.mem.buffer)
+			this._goRefCounts = []; // number of references that Go has to a JS value, indexed by reference id
+			this._ids = new Map();  // mapping from JS values to reference ids
+			this._idPool = [];      // unused ids that have been garbage collected
+			this.exited = false;    // whether the Go program has exited
 
 			// Pass command line arguments and environment variables to WebAssembly by writing them to the linear memory.
 			let offset = 4096;
@@ -444,7 +501,7 @@
 			const strPtr = (str) => {
 				const ptr = offset;
 				const bytes = encoder.encode(str + "\0");
-				new Uint8Array(mem.buffer, offset, bytes.length).set(bytes);
+				new Uint8Array(this.mem.buffer, offset, bytes.length).set(bytes);
 				offset += bytes.length;
 				if (offset % 8 !== 0) {
 					offset += 8 - (offset % 8);
@@ -458,17 +515,18 @@
 			this.argv.forEach((arg) => {
 				argvPtrs.push(strPtr(arg));
 			});
+			argvPtrs.push(0);
 
 			const keys = Object.keys(this.env).sort();
-			argvPtrs.push(keys.length);
 			keys.forEach((key) => {
 				argvPtrs.push(strPtr(`${key}=${this.env[key]}`));
 			});
+			argvPtrs.push(0);
 
 			const argv = offset;
 			argvPtrs.forEach((ptr) => {
-				mem.setUint32(offset, ptr, true);
-				mem.setUint32(offset + 4, 0, true);
+				this.mem.setUint32(offset, ptr, true);
+				this.mem.setUint32(offset + 4, 0, true);
 				offset += 8;
 			});
 
diff --git a/eg/windows/main.go b/eg/windows/main.go
index 73da02b..856cf50 100644
--- a/eg/windows/main.go
+++ b/eg/windows/main.go
@@ -17,7 +17,7 @@ var (
 	Height = 768
 
 	// Cascade offset for creating multiple windows.
-	Cascade      = render.NewPoint(10, 10)
+	Cascade      = render.NewPoint(10, 32)
 	CascadeStep  = render.NewPoint(24, 24)
 	CascadeLoops = 1
 
@@ -45,6 +45,20 @@ func main() {
 		panic(err)
 	}
 
+	// Menu bar.
+	menu := ui.NewMenuBar("Main Menu")
+	file := menu.AddMenu("Options")
+	file.AddItem("New window", func() {
+		addWindow(mw)
+	})
+	file.AddItem("Close all windows", func() {
+		OpenWindows -= mw.Supervisor().CloseAllWindows()
+	})
+
+	menu.Supervise(mw.Supervisor())
+	menu.Compute(mw.Engine)
+	mw.Pack(menu, menu.PackTop())
+
 	// Add some windows to play with.
 	addWindow(mw)
 	addWindow(mw)
@@ -95,7 +109,7 @@ func addWindow(mw *ui.MainWindow) {
 	Cascade.Add(CascadeStep)
 	if Cascade.Y > Height-240-64 {
 		CascadeLoops++
-		Cascade.Y = 24
+		Cascade.Y = 32
 		Cascade.X = 24 * CascadeLoops
 	}
 
diff --git a/eg/windows/main_wasm.go b/eg/windows/main_wasm.go
index e0aa1b0..f866519 100644
--- a/eg/windows/main_wasm.go
+++ b/eg/windows/main_wasm.go
@@ -24,7 +24,7 @@ var (
 	Height = 768
 
 	// Cascade offset for creating multiple windows.
-	Cascade      = render.NewPoint(10, 10)
+	Cascade      = render.NewPoint(10, 32)
 	CascadeStep  = render.NewPoint(24, 24)
 	CascadeLoops = 1
 
@@ -73,6 +73,20 @@ func main() {
 		height-lbl.Size().H-20,
 	))
 
+	// Menu bar.
+	menu := ui.NewMenuBar("Main Menu")
+	file := menu.AddMenu("Options")
+	file.AddItem("New window", func() {
+		addWindow(mw, frame, supervisor)
+	})
+	file.AddItem("Close all windows", func() {
+		OpenWindows -= supervisor.CloseAllWindows()
+	})
+
+	menu.Supervise(supervisor)
+	menu.Compute(mw)
+	frame.Pack(menu, menu.PackTop())
+
 	// Add some windows to play with.
 	addWindow(mw, frame, supervisor)
 	addWindow(mw, frame, supervisor)
@@ -85,6 +99,7 @@ func main() {
 			panic(err)
 		}
 
+		frame.Present(mw, frame.Point())
 		lbl.Present(mw, lbl.Point())
 		supervisor.Loop(ev)
 		supervisor.Present(mw)
diff --git a/functions.go b/functions.go
index 7ae0d5f..91f340e 100644
--- a/functions.go
+++ b/functions.go
@@ -41,6 +41,19 @@ func AbsoluteRect(w Widget) render.Rect {
 	}
 }
 
+// HasParent returns whether the target widget is a descendant of the parent.
+// This scans the parents of the widget recursively until it finds a match.
+func HasParent(w Widget, parent Widget) bool {
+	next, ok := w.Parent()
+	for ok {
+		if next == parent {
+			return true
+		}
+		next, ok = next.Parent()
+	}
+	return false
+}
+
 // widgetInFocusedWindow returns whether a widget (like a Button) is a
 // descendant of a Window that is being Window Managed by Supervisor, and
 // said window is in a Focused state.
diff --git a/menu.go b/menu.go
index 9aed60c..863607c 100644
--- a/menu.go
+++ b/menu.go
@@ -4,39 +4,78 @@ import (
 	"fmt"
 
 	"git.kirsle.net/go/render"
+	"git.kirsle.net/go/ui/theme"
 )
 
-// Menu is a rectangle that holds menu items.
+// MenuWidth sets the width of all popup menus. TODO, widths should be automatic.
+var MenuWidth = 180
+
+// Menu is a frame that holds menu items. It is the
 type Menu struct {
 	BaseWidget
 	Name string
 
-	body *Frame
+	supervisor *Supervisor
+	body       *Frame
+	items      []*MenuItem
 }
 
 // NewMenu creates a new Menu. It is hidden by default. Usually you'll
 // use it with a MenuButton or in a right-click handler.
 func NewMenu(name string) *Menu {
 	w := &Menu{
-		Name: name,
-		body: NewFrame(name + ":Body"),
+		Name:  name,
+		body:  NewFrame(name + ":Body"),
+		items: []*MenuItem{},
 	}
 	w.body.Configure(Config{
-		Width:       150,
-		BorderSize:  12,
+		Width:       MenuWidth,
+		Height:      100,
+		BorderSize:  0,
 		BorderStyle: BorderRaised,
-		Background:  render.Grey,
+		Background:  theme.ButtonBackgroundColor,
 	})
+	w.body.SetParent(w)
 	w.IDFunc(func() string {
 		return fmt.Sprintf("Menu<%s>", w.Name)
 	})
 	return w
 }
 
+// Children returns the child frame of the menu.
+func (w *Menu) Children() []Widget {
+	return []Widget{
+		w.body,
+	}
+}
+
+// Supervise the Menu. This will add all current and future MenuItem widgets
+// to the supervisor.
+func (w *Menu) Supervise(s *Supervisor) {
+	w.supervisor = s
+	for _, item := range w.items {
+		w.supervisor.Add(item)
+	}
+}
+
 // Compute the menu
 func (w *Menu) Compute(e render.Engine) {
 	w.body.Compute(e)
 
+	// TODO: ideally the Frame Pack Compute would fix the size of the body
+	// for the height to match the height of the menu items... but for now
+	// manually set the height.
+	var maxWidth int
+	var height int
+	for _, child := range w.body.Children() {
+		size := child.Size()
+		if size.W > maxWidth {
+			maxWidth = size.W
+		}
+		height += child.Size().H
+	}
+	w.body.Resize(render.NewRect(maxWidth, height))
+
 	// Call the BaseWidget Compute in case we have subscribers.
 	w.BaseWidget.Compute(e)
 }
@@ -51,19 +90,69 @@ func (w *Menu) Present(e render.Engine, p render.Point) {
 
 // AddItem quickly adds an item to a menu.
 func (w *Menu) AddItem(label string, command func()) *MenuItem {
-	menu := NewMenuItem(label, command)
+	menu := NewMenuItem(label, "", command)
+
+	// Add a Click handler that closes the menu when a selection is made.
+	menu.Handle(Click, w.menuClickHandler)
+
 	w.Pack(menu)
 	return menu
 }
 
+// AddItemAccel quickly adds an item to a menu with a shortcut key label.
+func (w *Menu) AddItemAccel(label string, accelerator string, command func()) *MenuItem {
+	menu := NewMenuItem(label, accelerator, command)
+
+	// Add a Click handler that closes the menu when a selection is made.
+	menu.Handle(Click, w.menuClickHandler)
+
+	w.Pack(menu)
+	return menu
+}
+
+// Click handler for all menu items, to also close the menu behind them.
+func (w *Menu) menuClickHandler(ed EventData) error {
+	if w.supervisor != nil {
+		w.supervisor.PopModal(w)
+	}
+	return nil
+}
+
+// AddSeparator adds a separator bar to the menu to delineate items.
+func (w *Menu) AddSeparator() *MenuItem {
+	sep := NewMenuSeparator()
+	w.Pack(sep)
+	return sep
+}
+
 // Pack a menu item onto the menu.
 func (w *Menu) Pack(item *MenuItem) {
+	w.items = append(w.items, item)
 	w.body.Pack(item, Pack{
-		Side: NE,
-		// Expand: true,
-		// Padding: 8,
+		Side:  N,
 		FillX: true,
 	})
+	if w.supervisor != nil {
+		w.supervisor.Add(item)
+	}
+}
+
+// Size returns the size of the menu's body.
+func (w *Menu) Size() render.Rect {
+	return w.body.Size()
+}
+
+// Rect returns the rect of the menu's body.
+func (w *Menu) Rect() render.Rect {
+	// TODO: the height reports wrong (0), manually add up the MenuItem sizes.
+	// This manifests in Supervisor.runWidgetEvents when checking if the cursor
+	// clicked outside the rect of the active menu modal.
+	rect := w.body.Rect()
+	rect.H = 0
+	for _, child := range w.body.Children() {
+		rect.H += child.Size().H
+	}
+	return rect
 }
 
 // MenuItem is an item in a Menu.
@@ -72,28 +161,71 @@ type MenuItem struct {
 	Label       string
 	Accelerator string
 	Command     func()
+	separator   bool
 	button      *Button
+
+	// store of most recent bg color set on a menu item
+	cacheBg render.Color
+	cacheFg render.Color
 }
 
 // NewMenuItem creates a new menu item.
-func NewMenuItem(label string, command func()) *MenuItem {
+func NewMenuItem(label, accelerator string, command func()) *MenuItem {
 	w := &MenuItem{
-		Label:   label,
-		Command: command,
+		Label:       label,
+		Accelerator: accelerator,
+		Command:     command,
 	}
 	w.IDFunc(func() string {
 		return fmt.Sprintf("MenuItem<%s>", w.Label)
 	})
 
 	font := DefaultFont
-	font.Color = render.White
+	font.Color = render.Black
 	font.PadX = 12
-	w.Button.child = NewLabel(Label{
-		Text: label,
-		Font: font,
+	font.PadY = 2
+
+	// The button child will be a Frame so we can have a left-aligned label
+	// and a right-aligned accelerator.
+	frame := NewFrame(label + ":Frame")
+	frame.Configure(Config{
+		Width: MenuWidth,
 	})
+	{
+		// Left of frame: menu item label
+		lbl := NewLabel(Label{
+			Text: label,
+			Font: font,
+		})
+		frame.Pack(lbl, Pack{
+			Side: W,
+		})
+
+		// On the right: accelerator shortcut key
+		if accelerator != "" {
+			accel := NewLabel(Label{
+				Text: accelerator,
+				Font: font,
+			})
+			frame.Pack(accel, Pack{
+				Side: E,
+			})
+		}
+	}
+
+	w.Button.child = frame
 	w.Button.Configure(Config{
-		Background: render.Blue,
+		BorderSize: 0,
+		Background: theme.ButtonBackgroundColor,
+	})
+
+	w.Button.Handle(MouseOver, func(ed EventData) error {
+		w.setHoverStyle(true)
+		return nil
+	})
+	w.Button.Handle(MouseOut, func(ed EventData) error {
+		w.setHoverStyle(false)
+		return nil
 	})
 
 	w.Button.Handle(Click, func(ed EventData) error {
@@ -104,3 +236,53 @@ func NewMenuItem(label string, command func()) *MenuItem {
 	// Assign the button
 	return w
 }
+
+// NewMenuSeparator creates a separator menu item.
+func NewMenuSeparator() *MenuItem {
+	w := &MenuItem{
+		separator: true,
+	}
+	w.IDFunc(func() string {
+		return "MenuItem<separator>"
+	})
+	w.Button.child = NewFrame("Menu Separator")
+	w.Button.Configure(Config{
+		Width:       MenuWidth,
+		Height:      2,
+		BorderSize:  1,
+		BorderStyle: BorderSunken,
+		BorderColor: render.Grey,
+	})
+	return w
+}
+
+// Set the hover styling (text/bg color)
+func (w *MenuItem) setHoverStyle(hovering bool) {
+	// Note: this only works if the MenuItem is using the standard
+	// Frame and Labels layout created by AddItem(). If not, this function
+	// does nothing.
+
+	// BG color.
+	if hovering {
+		w.cacheBg = w.Background()
+		w.SetBackground(render.SkyBlue)
+	} else {
+		w.SetBackground(w.cacheBg)
+	}
+
+	frame, ok := w.Button.child.(*Frame)
+	if !ok {
+		return
+	}
+
+	for _, widget := range frame.Children() {
+		if label, ok := widget.(*Label); ok {
+			if hovering {
+				w.cacheFg = label.Font.Color
+				label.Font.Color = render.White
+			} else {
+				label.Font.Color = w.cacheFg
+			}
+		}
+	}
+}
diff --git a/menu_bar.go b/menu_bar.go
new file mode 100644
index 0000000..7ba2baa
--- /dev/null
+++ b/menu_bar.go
@@ -0,0 +1,80 @@
+package ui
+
+import (
+	"fmt"
+
+	"git.kirsle.net/go/render"
+	"git.kirsle.net/go/ui/theme"
+)
+
+// MenuFont is the default font settings for MenuBar buttons.
+var MenuFont = render.Text{
+	Size:  12,
+	Color: render.Black,
+	PadX:  4,
+	PadY:  2,
+}
+
+// MenuBar is a frame that holds several MenuButtons, such as for the main
+// menu at the top of a window.
+type MenuBar struct {
+	Frame
+	name string
+
+	supervisor *Supervisor
+	buttons    []*MenuButton
+}
+
+// NewMenuBar creates a new menu bar frame.
+func NewMenuBar(name string) *MenuBar {
+	w := &MenuBar{
+		name:    name,
+		buttons: []*MenuButton{},
+	}
+	w.SetBackground(theme.ButtonBackgroundColor)
+	w.Frame.Setup()
+	w.IDFunc(func() string {
+		return fmt.Sprintf("MenuBar<%s>", w.name)
+	})
+	return w
+}
+
+// Supervise the menu bar, making its child menu buttons work correctly.
+func (w *MenuBar) Supervise(s *Supervisor) {
+	w.supervisor = s
+
+	// Supervise the existing buttons.
+	for _, btn := range w.buttons {
+		s.Add(btn)
+		btn.Supervise(s)
+	}
+}
+
+// AddMenu adds a new menu button to the bar. Returns the MenuButton
+// object so that you can add items to it.
+func (w *MenuBar) AddMenu(label string) *MenuButton {
+	btn := NewMenuButton(label, NewLabel(Label{
+		Text: label,
+		Font: MenuFont,
+	}))
+	w.buttons = append(w.buttons, btn)
+
+	// Pack and supervise it.
+	w.Pack(btn, Pack{
+		Side: W,
+	})
+	if w.supervisor != nil {
+		w.supervisor.Add(btn)
+		btn.Supervise(w.supervisor)
+	}
+	return btn
+}
+
+// PackTop returns the default Frame Pack settings to place the menu
+// at the top of the parent widget.
+func (w *MenuBar) PackTop() Pack {
+	return Pack{
+		Side:  N,
+		FillX: true,
+	}
+}
diff --git a/menu_button.go b/menu_button.go
new file mode 100644
index 0000000..e242572
--- /dev/null
+++ b/menu_button.go
@@ -0,0 +1,195 @@
+package ui
+
+import (
+	"fmt"
+
+	"git.kirsle.net/go/render"
+	"git.kirsle.net/go/ui/theme"
+)
+
+// MenuButton is a button that opens a menu when clicked.
+//
+// After creating a MenuButton, call AddItem() to add options and callback
+// functions to fill out the menu. When the MenuButton is clicked, its menu
+// will be drawn and take modal priority in the Supervisor.
+type MenuButton struct {
+	Button
+
+	name       string
+	supervisor *Supervisor
+	menu       *Menu
+}
+
+// NewMenuButton creates a new MenuButton (labels recommended).
+//
+// If the child is a Label, this function will set some sensible padding on
+// its font if the Label does not already have non-zero padding set.
+func NewMenuButton(name string, child Widget) *MenuButton {
+	w := &MenuButton{
+		name: name,
+	}
+	w.Button.child = child
+
+	// If it's a Label (most common), set sensible default padding.
+	if label, ok := child.(*Label); ok {
+		if label.Font.Padding == 0 && label.Font.PadX == 0 && label.Font.PadY == 0 {
+			label.Font.PadX = 8
+			label.Font.PadY = 4
+		}
+	}
+
+	w.IDFunc(func() string {
+		return fmt.Sprintf("MenuButton<%s>", name)
+	})
+
+	w.setup()
+	return w
+}
+
+// Supervise the MenuButton. This is necessary for the pop-up menu to work
+// when the button is clicked.
+func (w *MenuButton) Supervise(s *Supervisor) {
+	w.initMenu()
+	w.supervisor = s
+	w.menu.Supervise(s)
+}
+
+// AddItem adds a new option to the MenuButton's menu.
+func (w *MenuButton) AddItem(label string, f func()) {
+	w.initMenu()
+	w.menu.AddItem(label, f)
+}
+
+// AddItemAccel adds a new menu option with hotkey text.
+func (w *MenuButton) AddItemAccel(label string, accelerator string, f func()) *MenuItem {
+	w.initMenu()
+	return w.menu.AddItemAccel(label, accelerator, f)
+}
+
+// AddSeparator adds a separator to the menu.
+func (w *MenuButton) AddSeparator() {
+	w.initMenu()
+	w.menu.AddSeparator()
+}
+
+// Compute to re-evaluate the button state (in the case of radio buttons where
+// a different button will affect the state of this one when clicked).
+func (w *MenuButton) Compute(e render.Engine) {
+	if w.menu != nil {
+		w.menu.Compute(e)
+		w.positionMenu(e)
+	}
+}
+
+// positionMenu sets the position where the pop-up menu will appear when
+// the button is clicked. Usually, the menu appears below and to the right of
+// the button. But if the menu will hit a window boundary, its position will
+// be adjusted to fit the window while trying not to overlap its own button.
+func (w *MenuButton) positionMenu(e render.Engine) {
+	var (
+		// Position and size of the MenuButton button.
+		buttonPoint = w.Point()
+		buttonSize  = w.Size()
+
+		// Size of the actual desktop window.
+		Width, Height = e.WindowSize()
+	)
+
+	// Ideal location: below and to the right of the button.
+	w.menu.MoveTo(render.Point{
+		X: buttonPoint.X,
+		Y: buttonPoint.Y + buttonSize.H + w.BoxThickness(2),
+	})
+
+	var (
+		// Size of the menu.
+		menuPoint = w.menu.Point()
+		menuSize  = w.menu.Rect()
+		margin    = 8  // keep away from directly touching window edges
+		topMargin = 32 // keep room for standard Menu Bar
+	)
+
+	// Will we clip out the bottom of the window?
+	if menuPoint.Y+menuSize.H+margin > Height {
+		// Put us above the button instead, with the bottom of the
+		// menu touching the top of the button.
+		menuPoint = render.Point{
+			X: buttonPoint.X,
+			Y: buttonPoint.Y - menuSize.H - w.BoxThickness(2),
+		}
+
+		// If this would put us over the TOP edge of the window now,
+		// cap the movement so the top of the menu is visible. We can't
+		// avoid overlapping the button with the menu so might as well
+		// start now.
+		if menuPoint.Y < topMargin {
+			menuPoint.Y = topMargin
+		}
+
+		w.menu.MoveTo(menuPoint)
+	}
+
+	// Will we clip out the right of the window?
+	if menuPoint.X+menuSize.W > Width {
+		// Move us in from the right side of the window.
+		var delta = Width - menuSize.W - margin
+		w.menu.MoveTo(render.Point{
+			X: delta,
+			Y: menuPoint.Y,
+		})
+	}
+	_ = Width
+}
+
+// setup the common things between checkboxes and radioboxes.
+func (w *MenuButton) setup() {
+	w.Configure(Config{
+		BorderSize:  1,
+		BorderStyle: BorderSolid,
+		Background:  theme.ButtonBackgroundColor,
+	})
+
+	w.Handle(MouseOver, func(ed EventData) error {
+		w.hovering = true
+		w.SetBorderStyle(BorderRaised)
+		return nil
+	})
+	w.Handle(MouseOut, func(ed EventData) error {
+		w.hovering = false
+		w.SetBorderStyle(BorderSolid)
+		return nil
+	})
+
+	w.Handle(MouseDown, func(ed EventData) error {
+		w.clicked = true
+		w.SetBorderStyle(BorderSunken)
+		return nil
+	})
+	w.Handle(MouseUp, func(ed EventData) error {
+		w.clicked = false
+		return nil
+	})
+
+	w.Handle(Click, func(ed EventData) error {
+		// Are we properly configured?
+		if w.supervisor != nil && w.menu != nil {
+			w.menu.Show()
+			w.supervisor.PushModal(w.menu)
+		}
+		return nil
+	})
+}
+
+// initialize the Menu widget.
+func (w *MenuButton) initMenu() {
+	if w.menu == nil {
+		w.menu = NewMenu(w.name + ":Menu")
+		w.menu.Hide()
+
+		// Handle closing the menu when clicked outside.
+		w.menu.Handle(CloseModal, func(ed EventData) error {
+			ed.Supervisor.PopModal(w.menu)
+			return nil
+		})
+	}
+}
diff --git a/menu_test.go b/menu_test.go
new file mode 100644
index 0000000..16b304e
--- /dev/null
+++ b/menu_test.go
@@ -0,0 +1,83 @@
+package ui_test
+
+import (
+	"git.kirsle.net/go/ui"
+)
+
+// Example of using the menu widgets.
+func ExampleMenu() {
+	mw, err := ui.NewMainWindow("Menu Bar Example", 800, 600)
+	if err != nil {
+		panic(err)
+	}
+
+	// Create a main menu for your window.
+	menu := ui.NewMenuBar("Main Menu")
+
+	// File menu. Some items with accelerators, some without.
+	// NOTE: key bindings are up to you, the accelerators are
+	// purely decorative.
+	file := menu.AddMenu("File")
+	file.AddItemAccel("New", "Ctrl-N", func() {})
+	file.AddItemAccel("Open", "Ctrl-O", func() {})
+	file.AddItemAccel("Save", "Ctrl-S", func() {})
+	file.AddItem("Save as...", func() {})
+	file.AddSeparator()
+	file.AddItem("Close window", func() {})
+	file.AddItemAccel("Exit", "Alt-F4", func() {})
+
+	// Help menu.
+	help := menu.AddMenu("Help")
+	help.AddItemAccel("Contents", "F1", func() {})
+	help.AddItem("About", func() {})
+
+	// Give the menu bar your Supervisor so it can wire all
+	// events up and make the menus work.
+	menu.Supervise(mw.Supervisor())
+
+	// Compute and pack the menu bar against the top of
+	// the main window (or other parent container)
+	menu.Compute(mw.Engine)
+	mw.Pack(menu, menu.PackTop()) // Side: N, FillX: true
+
+	// Each loop you must then:
+	// - Call Supervisor.Loop() as normal to handle events.
+	// - Call Supervisor.Present() to draw the modal popup menus.
+	// MainLoop() of the MainWindow does this for you.
+	mw.MainLoop()
+}
+
+// Example of using the MenuButton.
+func ExampleMenuButton() {
+	mw, err := ui.NewMainWindow("Menu Button", 800, 600)
+	if err != nil {
+		panic(err)
+	}
+
+	// Create a MenuButton much as you would a normal Button.
+	btn := ui.NewMenuButton("Button1", ui.NewLabel(ui.Label{
+		Text: "File",
+	}))
+	mw.Place(btn, ui.Place{ // place it in the center
+		Center: true,
+		Middle: true,
+	})
+
+	// Add menu items to it.
+	btn.AddItemAccel("New", "Ctrl-N", func() {})
+	btn.AddItemAccel("Open", "Ctrl-O", func() {})
+	btn.AddItemAccel("Save", "Ctrl-S", func() {})
+	btn.AddItem("Save as...", func() {})
+	btn.AddSeparator()
+	btn.AddItem("Close window", func() {})
+	btn.AddItemAccel("Exit", "Alt-F4", func() {})
+
+	// Add the button to Supervisor for events to work.
+	btn.Supervise(mw.Supervisor())
+
+	// Each loop you must then:
+	// - Call Supervisor.Loop() as normal to handle events.
+	// - Call Supervisor.Present() to draw the modal popup menus.
+	// MainLoop() of the MainWindow does this for you.
+	mw.MainLoop()
+}
diff --git a/supervisor.go b/supervisor.go
index 00b8d31..151e122 100644
--- a/supervisor.go
+++ b/supervisor.go
@@ -32,6 +32,7 @@ const (
 	CloseWindow
 	MaximizeWindow
 	MinimizeWindow
+	CloseModal
 
 	// Lifecycle event handlers.
 	Compute // fired whenever the widget runs Compute
@@ -45,6 +46,9 @@ type EventData struct {
 
 	// Engine is the render engine on Compute and Present events.
 	Engine render.Engine
+
+	// Supervisor is the reference to the supervisor who sent the event.
+	Supervisor *Supervisor
 }
 
 // Supervisor keeps track of widgets of interest to notify them about
@@ -58,6 +62,9 @@ type Supervisor struct {
 	clicked  map[int]bool        // map of widgets being clicked
 	dd       *DragDrop
 
+	// Stack of modal widgets that have event priority.
+	modals []Widget
+
 	// List of window focus history for Window Manager.
 	winFocus  *FocusedWindow
 	winTop    *FocusedWindow // pointer to top-most window
@@ -76,6 +83,7 @@ func NewSupervisor() *Supervisor {
 		widgets:  map[int]WidgetSlot{},
 		hovering: map[int]interface{}{},
 		clicked:  map[int]bool{},
+		modals:   []Widget{},
 		dd:       NewDragDrop(),
 	}
 }
@@ -169,14 +177,18 @@ func (s *Supervisor) Loop(ev *event.State) error {
 	// Run events in managed windows first, from top to bottom.
 	// Widgets in unmanaged windows will be handled next.
 	// err := s.runWindowEvents(XY, ev, hovering, outside)
-	handled, err := s.runWidgetEvents(XY, ev, hovering, outside, true)
-	if err == ErrStopPropagation || handled {
-		// A widget in the active window has accepted an event. Do not pass
-		// the event also to lower widgets.
-		return err
+	// Only run if there is no active modal (modals have top priority)
+	if len(s.modals) == 0 {
+		handled, err := s.runWidgetEvents(XY, ev, hovering, outside, true)
+		if err == ErrStopPropagation || handled {
+			// A widget in the active window has accepted an event. Do not pass
+			// the event also to lower widgets.
+			return err
+		}
 	}
 
 	// Run events for the other widgets not in a managed window.
+	// (Modal event priority is handled in runWidgetEvents)
 	s.runWidgetEvents(XY, ev, hovering, outside, false)
 
 	return nil
@@ -233,13 +245,21 @@ func (s *Supervisor) Hovering(cursor render.Point) (hovering, outside []WidgetSl
 //    0: widgets NOT part of a managed window. On this pass, if a widget IS
 //       a part of a window, it gets no events triggered.
 //    1: widgets are part of the active focused window.
-func (s *Supervisor) runWidgetEvents(XY render.Point, ev *event.State, hovering, outside []WidgetSlot, toFocusedWindow bool) (bool, error) {
+func (s *Supervisor) runWidgetEvents(XY render.Point, ev *event.State,
+	hovering, outside []WidgetSlot, toFocusedWindow bool) (bool, error) {
 	// Do we run any events?
 	var (
 		stopPropagation bool
 		ranEvents       bool
 	)
 
+	// Do we have active modals? Modal widgets have top event priority given
+	// only to the top-most modal.
+	var modal Widget
+	if len(s.modals) > 0 {
+		modal = s.modals[len(s.modals)-1]
+	}
+
 	// If we're running this method in "Phase 2" (to widgets NOT in the focused
 	// window), only send mouse events to widgets if the cursor is NOT inside
 	// the bounding box of the active focused window. Prevents clicking "thru"
@@ -273,7 +293,8 @@ func (s *Supervisor) runWidgetEvents(XY render.Point, ev *event.State, hovering,
 		// If the cursor is inside the box of the focused window, don't trigger
 		// active (hovering) mouse events. MouseOut type events, below, can still
 		// trigger.
-		if cursorInsideFocusedWindow {
+		// Does not apply when a modal widget is active.
+		if cursorInsideFocusedWindow && modal == nil {
 			break
 		}
 
@@ -287,6 +308,14 @@ func (s *Supervisor) runWidgetEvents(XY render.Point, ev *event.State, hovering,
 			continue
 		}
 
+		// If we have a modal active, validate this widget is a child of
+		// the modal widget.
+		if modal != nil {
+			if !HasParent(w, modal) {
+				continue
+			}
+		}
+
 		// Check if the widget is part of a Window managed by Supervisor.
 		isManaged, isFocused := widgetInFocusedWindow(w)
 
@@ -344,6 +373,14 @@ func (s *Supervisor) runWidgetEvents(XY render.Point, ev *event.State, hovering,
 			w  = child.widget
 		)
 
+		// If we have a modal active, validate this widget is a child of
+		// the modal widget.
+		if modal != nil {
+			if !HasParent(w, modal) {
+				continue
+			}
+		}
+
 		// Cursor is not intersecting the widget.
 		if _, ok := s.hovering[id]; ok {
 			handle(w.Event(MouseOut, EventData{
@@ -360,6 +397,16 @@ func (s *Supervisor) runWidgetEvents(XY render.Point, ev *event.State, hovering,
 		}
 	}
 
+	// If a modal is active and a click was registered outside the modal's
+	// bounding box, send the CloseModal event.
+	if modal != nil && !XY.Inside(AbsoluteRect(modal)) {
+		if ev.Button1 {
+			modal.Event(CloseModal, EventData{
+				Supervisor: s,
+			})
+		}
+	}
+
 	// If a stopPropagation was called, return it up the stack.
 	if stopPropagation {
 		return ranEvents, ErrStopPropagation
@@ -397,11 +444,28 @@ func (s *Supervisor) Present(e render.Engine) {
 
 	// Render the window manager windows from bottom to top.
 	s.presentWindows(e)
+
+	// Render the modals from bottom to top.
+	if len(s.modals) > 0 {
+		for _, modal := range s.modals {
+			modal.Present(e, modal.Point())
+		}
+	}
 }
 
-// Add a widget to be supervised.
+// Add a widget to be supervised. Has no effect if the widget is already
+// under the supervisor's care.
 func (s *Supervisor) Add(w Widget) {
 	s.lock.Lock()
+
+	// Check it's not already there.
+	for _, child := range s.widgets {
+		if child.widget == w {
+			return
+		}
+	}
+
+	// Add it.
 	s.widgets[s.serial] = WidgetSlot{
 		id:     s.serial,
 		widget: w,
@@ -409,3 +473,40 @@ func (s *Supervisor) Add(w Widget) {
 	s.serial++
 	s.lock.Unlock()
 }
+
+// PushModal sets the widget to be a "modal" for the Supervisor.
+//
+// Modal widgets have top-most event priority: mouse and click events go ONLY
+// to the modal and its descendants. Modals work as a stack: the most recently
+// pushed widget is the active modal, and popping the modal will make the
+// next most-recent widget be the active modal.
+//
+// If a Click event registers OUTSIDE the bounds of the modal widget, the
+// widget receives a CloseModal event.
+//
+// Returns the length of the modal stack.
+func (s *Supervisor) PushModal(w Widget) int {
+	s.modals = append(s.modals, w)
+	return len(s.modals)
+}
+
+// PopModal attempts to pop the modal from the stack, but only if the modal
+// is at the top of the stack.
+//
+// A widget may safely attempt to PopModal itself on a CloseModal event to
+// close themselves when the user clicks outside their box. If there were a
+// newer modal on the stack, this PopModal action would do nothing.
+func (s *Supervisor) PopModal(w Widget) bool {
+	// only can pop if the topmost widget is the one being asked for
+	if len(s.modals) > 0 && s.modals[len(s.modals)-1] == w {
+		modal := s.modals[len(s.modals)-1]
+		modal.Hide()
+
+		// pop it off
+		s.modals = s.modals[:len(s.modals)-1]
+
+		return true
+	}
+
+	return false
+}
diff --git a/widget.go b/widget.go
index dedac93..d68bad8 100644
--- a/widget.go
+++ b/widget.go
@@ -309,8 +309,13 @@ func (w *BaseWidget) Hidden() bool {
 		return true
 	}
 
-	if parent, ok := w.Parent(); ok {
-		return parent.Hidden()
+	// Return if any parents are hidden.
+	parent, ok := w.Parent()
+	for ok {
+		if parent.Hidden() {
+			return true
+		}
+		parent, ok = parent.Parent()
 	}
 
 	return false
diff --git a/window.go b/window.go
index 8d33b67..6ece7a8 100644
--- a/window.go
+++ b/window.go
@@ -296,6 +296,12 @@ func (w *Window) SetMaximized(v bool) {
 	}
 }
 
+// Close the window, hiding it from display and calling its CloseWindow handler.
+func (w *Window) Close() {
+	w.Hide()
+	w.Event(CloseWindow, EventData{})
+}
+
 // Children returns the window's child widgets.
 func (w *Window) Children() []Widget {
 	return []Widget{
diff --git a/window_manager.go b/window_manager.go
index f9e7822..14df10b 100644
--- a/window_manager.go
+++ b/window_manager.go
@@ -164,6 +164,21 @@ func (s *Supervisor) IsPointInWindow(point render.Point) bool {
 	return false
 }
 
+// CloseAllWindows closes all open windows being managed by supervisor.
+// Returns the number of windows closed.
+func (s *Supervisor) CloseAllWindows() int {
+	var (
+		node = s.winFocus
+		i    = 0
+	)
+	for node != nil {
+		i++
+		node.window.Hide()
+		node = node.next
+	}
+	return i
+}
+
 // presentWindows draws the windows from bottom to top.
 func (s *Supervisor) presentWindows(e render.Engine) {
 	item := s.winBottom