Halo creators Bungie have given the official nod to Aleph One , fan-made updates and remakes of the originally Mac-only Marathon series. The project reached version 1.0 in early December, with all three games now available for free. It's an impressive update, too: all three games include HD texture packs, network play, and work on modern operating systems.
They're exploration-based FPS games that look a little like Doom but play rather differently. From the beginning, Bungie were more interested in narrative than combat, and it shows: weapons and enemies are fairly standard fare, but its doomed starships and alien worlds still retain a bit of their old atmosphere. There's more writing than you'd expect, too, with world building-handled by AI-controlled computer terminals that feed out in-character plot and location info.
Marathon 2 even has voice-acted, short-lived teammates that fight alongside you for brief periods before biting the dust or teleporting away. The games feel like a glimpse into a parallel evolution of the FPS, one that - for better or worse - did a better job of anticipating the explosions-and-exposition future of the genre than anything id were making at the time.
As a package, it's something of a museum piece: but a well-curated one that's worth getting to know. The games themselves are polished, fun, and even creepy from time to time - just be willing to re-learn how to run around with the map open pressing use on everything. A note of warning: some of Marathon 2's menu noises sound exactly like an incoming Steam message. Don't be fooled! Your friends aren't really talking to you. Happy New Year.