Here is the my first (and probably not last) port of famitone2 to gameboy (for rgbds). It uses zombie mode and closely matches the NES version. You will use famitracker to write the songs.
See usage.txt for details.
https://github.com/nesdoug/famitoneGB
Famitone2 has been ported to Gameboy
Famitone2 has been ported to Gameboy
nesdoug.com -- blog/tutorial on programming for the NES