Before Bungie became part of Microsoft, they produced games like 1994’s Marathon.  It revolves around a spaceship, the Marathon, that’s invaded by aliens.  You’re part of the crew, tasked with the job of defending the ship so that the AI’s (artificial intelligences) that control it can marshal the ship’s defenses.

I assumed that the game was gone, since it hasn’t been ported for Mac OS X, though lo and behold, not only is Marathon (and the other two parts of the saga: Marathon: Durandal, and Marathon: Infinity) available for Apple, but it’s also available for Windows and Linux!

Download and enjoy the retro alien-fighting goodness.