Features:

• Yamaha YM2151 (OPM) 4 operator FM sound chip emulation.
• Supports MIDI CCs.

"OPM chip was popular in the 1980s and early 1990s. Videogame fans will most likely be familiar with the Sega Genesis (Megadrive), whose sound chip is a slight variation on the OPM - the OPN. The chip has also been used in countless arcade games including Paperboy, Outrun, Metal Slugs 1-5, and Street Fighter II."

VOPM is free, open source.