AssaultCube…
AssaultCube, formerly ActionCube, is a free first-person-shooter based on the game Cube. Set in a realistic looking environment, as far as that´s possible with this engine, while gameplay stays fast and arcade. This game is all about team oriented multiplayer fun.
…an 19MB small, 56k modem capable, OpenSource, multiplayer & singleplayer Shooter
minimum hardware: CPU 800 MHz,RAM 256,GRAM 32,56K modem.