This is what German hacker/student/musician Tob, who created the cool NitroTracker old-school tracker app for the DS has been working on: Software to turn put easy-to-use MIDI into the Nintendo DS using WiFi. Previously, you've had to use hardware. The DS obviously sucks as a keyboard, but is great as a little X-Y controller like a Kaoss Pad, and presumably there's no reason why he can't build a simple XOX drum programmer, a little Lemur clone, or even a virtual Monome. Tob is still developing the software - as you can see from the video, it's in a pretty early stage - but it will be released ASAP. And even if you don't have a DS, stick with this video long enough to hear the guy playing 'We Will Rock You' though the onboard sounds..