The Smule Ocarina app for the iPhone would be worth the 99 cents even if didn't boast a Zelda mode: it turns your iPhone into a musical wind instrument, where playing is accomplished by the fingering of digital valves coordinated with blowing into the microphone. It's also a social application: you can tap a globe icon and hear what other Ocarina players are playing, all over the world.
I'm eager to try it, but the disclaimer on the front page is a bit strange: "Optimized for 3G phones; for first generation phones we recommend upgrading to the 2.2 firmware when it becomes available." Huh. I wonder what's up with that.
Update: I can't play worth a damn, but this is pretty neat. The Global View, in which you can listen to other users playing, is particularly impressive: a fluid, rotatable globe spraying whirling ionic fountains of music.