Earlier this year, Bungie's 1990s sci-fi shooter, Marathon , came to Steam for free . And Marathon 2 followed in July. But this series is a trilogy.

Where's the third one? I want the thir-- oh, it's here now. Yesterday, the final game, Marathon Infinity trickled onto the storefront , offering a neat little bundle for fans of retro shooters. But it's also a reminder that we've yet to see more of Bungie's upcoming reboot.

As a finale, Infinity followed closely after the second game, coming out in 1996, back when sequels were released not even a year apart. It adds bits and pieces to an ongoing story about warring alien factions and an AI gone rogue. Squint and you can see that Bungie have been rewriting the same sci-fi tale for decades, the broad strokes storytelling of their games rhyming in noticeable ways even as the mechanical components evolve.

(For a good breakdown of Marathon as a shooter, and its place in FPS history, I can recommend this video by Errant Signal .) It's also worth pointing out that the entire set of Marathons have been freely available for decades thanks to the work of the developers of the Aleph One port, an open source project that kept these aged FPS games going. They've now simply brought the full trilogy to Valve's popular platform for the first time, it seems with Bungie's blessings.

Like its predecessors, Marathon Infinity is listed on Steam as "Classic Marathon Infinity" - the "classic" no doubt appended to distinguish these from the upcoming reb.