Bungie Studios first started on the Apple Macintosh. They had a few early underground games and became popular with Macintosh users with Marathon. Unknown to most Xbox and PC users, Marathon was Macintosh-only until Aleph One was released, allowing Windows users to play Marathon on their PC. (Previously, only the second game in the trilogy was ported to PC. Now you can play them all.)
Bungie became really popular with the Xbox crowd after Microsoft bought them out while they were working on Halo for the Macintosh. Later Halo was ported to PC and Macintosh by Gearbox Software (PC and Mac code) and Aspyr Media (Mac porter).