Anyone else remember Marathon? It was a first-person shooter Bungie made back in the mid-90s, BEFORE they got famous from Halo. It was made for the Macintosh computers, presumably to compete with the popularity of Doom on PCs with DOS and Windows. Three games were made: Marathon (1994,) Marathon 2: Durandal (1995) and Marathon Infinity (1996.) Years later, all three games would be released as freeware and ported to Windows, Mac OS X, and Linux. I own all three games for Windows. Marathon had several motifs that would later reappear in Halo, such as AI rampancy and many cryptic references to the number seven. These games are widely considered to be a spiritual prequel to the Halo games, despite taking place in separate fictional universes.
Fun fact: My tagline, "frog blast the vent core!" is a line from Marathon 2: Durandal. It is a nonsense phrase shouted by enemy constructs called "simulacrums" who look like friendly marines, but actually run at you and explode. I guess kind of like the infamous Suicide Grunts from Halo 3 and Halo: Reach.