I've been in a gaming midlife crisis lately, as I await Christmas (when I will be getting a Wii) - so I started to check out the mods for games I own. I was originally looking for a sci-fi conversion for Warcraft III, which I couldn't find.
I found this this. It's called Damnation, and it is a single player mod for Unreal Tournament 2004. It's a several level long Western steampunk FPS/3rd Person campaign - and it's damn good. The 3rd person focus, which I thought would suck, is wicked. Slick jumps, platforming, etc combine with the ability to possess enemy troops and blow the fecal matter out of 'em with a steam powered sniper. Add in some giant robots and a scantily clad Indian girl, you've got one hell of a game.
I also found this video of a Homeworld 2 to EVE Online RTS conversion. It is still in development, and the development doesn't look like it is going anywhere. Even so, it looks wicked. Too bad it is not going to be finished any time soon.