Bungie's seminal first-person shooter, Marathon, is now available for the iPad. But this port isn't Bungie's work -- it was put together by fan Daniel Blezek using Marathon source code.
The project, which has Bungie's blessing, is free to download. If you want to play it with fancier high definition graphics, though, you'll have to pay $3.99 for an upgrade package.
Speaking of Bungie, today's Bungie Day -- there's a whole bunch of stuff going on over at Bungie.net. Check it out.