Pixelh8 Music Tech Pro Performer Synthesizer is software that runs on an unmodified Game Boy Advance or Nintendo DS, enabling you to be able to control the on board sound, turning the GBA/DS into a real time instrument. Based on the original Game Boy Music Tech V1.0, Pro Performer offers hundreds more options and possible sounds.

Thanks to http://www.nintendomax.com/viewtopic.php?t=11076&f=27 for the news.