Source: vorc.org
MPX stands for MultiPlay-X. It's a music replayer for MSX2 computers and higher, and it enables you to play (MML-based) music files. Supported formats are OPX, BGM, MPK, MGS and BGR. The player comes with a neat interface for file-browsing.
Relevant link: www6.plala.or.jp/takkuweb/msx/index.html
