The Trackpad Magic app lets you play various instruments with the Magic Trackpad or MacBook’s Trackpad. It also features a variety of graphical effects and several [wikipop]musical scales[/wikipop]. Pressing the T key shows a grid to aid note finding. Pressing the I key cycles through the scales. The Doe Ray Me scale puts the G in the middle of the trackpad. With the C on the left edge you can pick your way through [wikipop]Twinkle Twinkle Little Star[/wikipop]. Turning off the grid and doing it blindfolded in the dark earns extra points 😉