Team Fortress Classic, one of the first mods released for Half-Life. Released in April of 1999, it was sort of a semi-sequel to the popular Team Fortress for Quake. It became quite popular, although not even close to Counter-Strike, and still holds a couple hundred people on Steam daily. At first, Team Fortress Classic is a wacky game with crazy physics and imbalanced classes, and it is. But underneath lies some very fun gameplay mechanics. The game has a bit of a learning curve in order to perform all of the crazy feats that you may see some players do, but it's well worth it as you have complete control over your character. Rocket Jumping, Concussion jumping, and much more. One of the best clan games I've played. For ten bucks, TFC is well worth it.