These are some music files in YMST format for MYST, the YM2149 soundchip
emulator for Atari ST. These tunes can be played with EaglePlayer or
DeliTracker on Amiga, or directly played on Atari ST.

You can get modules (re)source code from the Wanted Team page:

http://amiga.emucamp.com/wt/wt.html