All kinds of self-published stuff, lots of which later became commercial. You will have heard of some of it, for sure. Darude - Sandstorm? That was from there. DragonForce were big in the power metal category. The band that became Linkin Park came from there. And then hundreds of thousands of indie artists (including an earlier me).

The RIAA's action there destroyed vast amounts of music, pretty much the equivalent of if someone just aggressively deleted Bandcamp and Soundcloud put together and everything on it because they were upset they didn't control it all. I will never forgive them for that.