Generations Arena is a class-based modification for Quake III Arena created by Wirehead Studios. The twist, and the relation to Doom, is that the four new classes are based upon previous id Software games. Unlike Generations for Quake II, Generations Arena contains no copyrighted material from previous games, though there are some classic maps that have been recreated from scratch.
Slipgate (Quake) and Strogg (Quake II) classes play quite authentically. The Doom class is spot on in weaponry, but now utilizes true freelook, ducking, jumping and the Quake III air physics to give a fresh feel to it (and for balance reasons). The Earth class is very loosely based on the Macintosh version of Wolfenstein 3D, with some creative liberties. Finally, the Arena Gladiator class represents the normal Quake III class, whose only new feature is a brand new BFG.