Electroplankton

Electroplankton is a "game" for Nintendo DS that is really an interactive art and music installation in software. The official website has a very nice video overview of the work of artist Toshio Iwai, inventor of Electroplankton, from 1984 to present:

http://electroplankton.com/

To view the video, click the blue circle in the middle, wait for
Shockwave to load, click the 4th bubble from the left, then click the
4th link from the top (above the middle blue link). It starts with
some amazing flipbook animated art, then goes on to show Iwai's other
art projects.

I got these instructions from the Cheap Ass Gamer forum

Electroplankton was released only to the Japanese market, but there are a number of specialty/import shops that sell it to non-Japanese. The game is reportedly easy enough to learn and play for English readers. One thing it can do that LSDJ and Nanoloop, to my knowledge, can't is sample audio (via the DS mic) and play it back in realtime.

This is an English-language preview of the game with lots of video demos:

http://ds.ign.com/articles/603/603336p2.html

My first encounter with Game Boy music-making was a few years ago when I got a Game Boy Color to try out Nanoloop and Little Sound DJ, two music-making cartridges for Game Boy. I didn't get far with it, but Electroplankton has revived my interest in making music with a handheld Nintendo game console. There is an international Game Boy music making scene, though mostly underground.