A free, open-source version of Halo developer Bungie’s classic Marathon trilogy has been released online. Available for Linux, Mac and PC, the pack contains an updated version of the engine, a fan remake of the first Marathon, and lovingly HD remastered versions of Marathon 2 and Marathon Infinity. The new versions sport modern features like online multiplayer including co-op; control pad support; and OpenGL shader functionality. You can grab the pack here. The Marathon series of shooters kicked off in 1994 and wrapped up in 1996, predating Halo by five years.