Topic: Multichannel/unusual PC speaker music
By some reason, PC speaker music most often was limited to the basic square wave. The common best tricks were to interleave a few channels with quite horrible buzz (Lotus III, or occasionally interrupt one channel of sound with another (Monkey Island 2). Rarely a game attempted to put at least some expression into music, like Ski or Die! (slides and vibrato).
There were rare attempts to go beyond this, with true synthesizers/multichannel engines, though, which is totally possible (there is WAV/MOD/MP3 players for PC Speaker, after all), and always interesting to see. Thought to list a ones that I managed to find so far, while I'm researching this field.
Moon Patrol (1983) - a weird one, has three kinds of music, look for end stage and game over
Rollo and the Brush Brothers (1984)
Styx (1984) - no music, but unusual sounds
Music Construction Set (1984?)
Saboteur II (1987)
Sid Meier's Pirates (1987)
F-15 Strike Eagle II (1989)
Fantasy World Dizzy (1989)
Hard Drivin' (1989)
Turbo Outrun (1990)
Should be noted that many of these videos has been made using DosBox, and it does not emulate PC Speaker well enough, introducing noticeable sound distortions in such complex routines. Saboteur II and Hard Drivin' suffered a lot.