Kerbal Space Program.
I transferred it over to Steam, made the BCSP* flag, got in, and messed about in the career and science modes. I missed this game, only reason I stopped playing (over a year ago I believe?) was because my computer couldn't run it very well any more. Well, I did some tweaking and managed to get it to run at a playable framerate, so yay!
Last time, I couldn't really do much aside from orbit and land on Mun, but I hope to be a bit more ambitious this time around.
*Black Cat Space Program ... kinda just thought it up on the spot.