Created by Bungie, this game is the father of Halo. You are a security officer who is called to eradicate the Phfor inside the UESC Marathon. However, things are never that simple when a rampant AI called Durandal kidnaps you and forces you to do whatever he says. This game is similar to Doom, yet has some elements that are carried over to Halo…. There is no lag whatsoever when played with the “software” engine, and little issues on “OpenGL”. This game also has full fledged multiplayer with cooperative mode and a wide variety of competitive game types.
The Marathon Trilogy is free and open source. It is compatible with Mac, Linux, and Windows.