From SuperCollider wiki
SC 2 was the MacOS 9 version of SuperCollider. It was the most common while MacOS 9 was in its heyday.
There was also a free player version at the times when SC was non-free software, called SCPlay, it is not needed anymore.
If you want to use sc2 under os x, you will need to find drivers.
Midi can also be ported to Classic OMS, (didn't test it):