Before Bungie blew up with the Halo franchise, it worked on a sci-fi first person trilogy called Marathon. As a surprise gift for the holiday season, all three games are being released for free alongside an open-source version of the Marathon 2 engine, Aleph One.
Included in the release is Marathon 2, Marathony Infinity, and a "fan remake" of the original Marathon. A few simple clicks will let you download a version for PC, Mac, and even Linux, too.
Aleph One updates Bungie's original games with OpenGL shader support, internet co-op and multiplayer, "modern mouse-look" and support for game pads.
Each of the games have been updated with high-resolution graphics. However, the original game gets the most significant overhaul. Marathon's HUD receives a modern HUD facelift and "extensive changes to the scenario to create the most authentic Marathon experience since 1994."
So, what are you waiting for? To download Aleph One, click here.