FUDI Kaos DS
From GameBrew - a wiki dedicated to Video Game Homebrew.
FUDIKaosDS is a music application that allows you to use your NDS as a Kaospad style input to send all touch-pad events and button event messages over the wifi to your music program.
The main use-case for this software is controlling Pure Data patches from the NDS touchscreen in order to make music.
It's intended as a replacement for complicated MIDI controller hardware, or an expensive Kaospoad in situations where more portability is required, such as when travelling. It communicates on the local wifi network using the FUDI protocol supported by Pure Data. Apparently you can use it with Max/MSP too, and there is an included .pat file to do this which some people have used successfully.