Fallout: The Frontier is an in-development mod for Fallout: New Vegas that doesn't just introduce new weather, weapons, quests and enemies, it takes the game to a space station.
We actually saw this mod around a year ago, and back then the big deal was that it featured winter snow and some serious expansion to what Bethesda's creaky ol' Gamebryo engine was capable of in terms of scripting and animation. Now, though, it's sections set on a space station that catch the eye, not just for the different look and feel, but for those gravity effects.
I'm digging the ability to man turrets and drive tanks, too.
The Frontier isn't done, and being an ambitious user-made thing carries the regular caveat of "this may never be done", but if it's still being worked on for this long and being improved and refined, who knows, we may actually get our hands on it some day.
UPDATE: Here's a look at the space station mission's intro: