Comment Marathon and the Halo Series (Score 5, Informative) 105
As someone already noted, the Marathon series was made by Bungie.
By the time Bungie was bought by Microsoft, much of Halo's building blocks were done, a game originally designed for both Macs and PCs.
There's plenty of Marathon homages in the original Halo (haven't yet played 2 or 3 myself). First, look on Captain Keyes's uniform for the Marathon symbol at the game's starting adventure on the bridge. Just as you leave the captain, look on the bulletin board at the entrance: An ad there says "Colony Ship for Sale" (a reference to a Marathon game level). Cortana, the AI, is another name that parallels the name of another mystical sword, Durandal (Marathon's sassy AI). See http://halo.wikia.com/wiki/List_of_Marathon_references_in_Halo for more.
Marathon was among the first (if not the first) FPS with multiplayer support (thanks to the Mac OS local networking) as well as establishing the convention of using the mouse for head-target movement. The concept of the Vidmaster (See http://marathon.bungie.org/vidmaster/ ) (using the weakest weapon at the game's highest difficulty to completion) was a Marathon first.