One Must Fall: Battlegrounds is a PC-only 3d fighting game developed by Diversions Entertainment.
Players takes control of a giant robot that does battle with others in many different arenas. There is a single player campaign mode for players, but the main draw is the 16 player simultaneous multiplayer.
Not only do players have to choose which robot to control, but which pilot to control it. The pilot determines the agility, overall strength, and endurance of the robot.