The Rain has released DSMidi for the Nintendo DS, here the release info:
The demo uses the DS's touch screen to control MIDI CC's 1 and 2 from the X and Y axis.. much like touch controllers like the Korg Kaoss Pad.
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He is also working on dSTAR Sequencer, heres the info on that project:
I have been hard at work the past couple of weeks creating a MIDI sequencer that uses my MIDI library and hardware hack for the Nintendo DS.
The dSTAR Sequencer will be an x0x like sequencer with drawable bar graph sequence lines. Here's a screen shot of the current unfinished beta version.
More info at his homepage