Thomas Mogensen not only composed a ton of awesome C64 tunes, he also composed for a few Game Boy Color games in the late 90’s. This page contains all the work he has done, including demo tunes.
The process of creating these tunes actually began in FastTracker 2. Thomas composed the tunes using samples from a Game Boy Color. The saved XM files were then converted to Game Boy Color binaries using a tool coded by Thomas Egeskov Petersen. The Game Boy Color hardware has two square wave channels, one wave channel, and one noise channel, but note that most in-game level tunes only use two voices.
Everything has been converted from the original XM files to MP3 for easy listening.