There's this mod that came out a while back for Half Life. Can't remember the name, but it's one of these Rainbow 6 conversion type things. Last time I played with it, it wasn't very finished. Hard to tell the models apart and very confusing weapons and ammo and the like. It was a ton of fun on a LAN, but one of my buddies wrote this little cheat that made all the models really bright, so the next time we played it wasn't much fun.
I hear it caught on, on this "Intarweb" I keep hearing about. Dammit, what was that called?