HIDUINO: Your Arduino is Now A MIDI Interface: "[Dimitri Diakopoulos] dropped into our tip line to let us know his HIDUINO project. The HIDUINO is a set of firmware for the ATmega8u2 used in the new revisions of the Arduino (Uno, and Mega2560 for example). Once the HIDUINO is loaded your Arduino can show up as any HID compliant device you wish, no extra drivers necessary. This means that using this firmware, music software such as Max, Ableton, Reaktor etc can read and write MIDI directly to/from the Arduino. Currently the project is for direct USB-MIDI communication but could be altered to act as a variety of HID devices."
'via Blog this'