AwesomeIf you have a DS and a card for homebrew, you need to check this out. Guess it was released in 2006 and no one noticed till now, but its surprisingly awesome. You make chiptune music with it, but you need no skill to do so. Seriously. A beat plays automatically, and you just touch the stylus around on the bottom screen to play notes. Different positions on the screen change pitch and such, but its all set to sound "right" with the beat.
Try it out if you're able. Its cool.