Elysia, manufacturer of both hardware and software studio gear, has published a YouTube video tutorial on sidechain compression.
A spokesperson had this to say, "Sidechain compression... what can we use it for? This tutorial shows some of the most favored sidechain tips and tricks, both in hardware and software: Groove compression, ducking and frequency dependent compression. Make things move!"
Gaz Williams has one and he brought it round
Eurorack module puts General MIDI sound set under creative CV control