LSDJ (little sound DJ) is a tracker for the Gameboy designed for live use. Compatibility with various gameboy models exists (GBA, monochrome gameboy and color gameboy) It's a paid tool, but demo releases are provided in ROM form so that you try on an emulator before you buy a cartridge.
It use 4 channels, 2 squares, 1 wav and 1 noise channel. You can module each channel an create your instruments with little variation in the settings. The WAV channel also support tiny synth waves and samples too. It comes with pack of classic drum set such as TR-606, TR-909, etc. In the WAV channel your able to use a little programmable speech with 59 phonems to create ""voices"".
You can sync 2 LSDJ or LSDJ with Nanoloop. Or you can sync with MIDI. Also having a "huge" ammount of peers willing to help you with mods, effects, and little tricks here and there.
The demo is available to download HERE
For more information go to http://www.littlesounddj.com/