Digital Sound and Music Interface is an old project of mine (co-authored by Jussi Lahdenniemi) from the early 90's. It is, as its name states, a library for producing music and sound effects in (DOS) applications. Back in the day it was licensed to several commercial games, most notably Disney's Lion King and Aladdin PC games.
DSMI supports several "module file" formats and internally converts them all to a custom AMF format (for Advanced Module Format).
DSMI was used as a basis for the Dual Module Player application (DMP) which allowed users to play (originally) both MOD and STM (Scream Tracker) formats, hence the name. Later on more formats were added. DMP was at its time the most popular module player on the PC DOS platform (see it in action). It was licensed as "card ware", which meant I received hundreds of post cards from users all around the world 😄
Enjoy browsing some old source code (which might predate your birth if you were born after 1993)!