Note that the below hasn't been updated since July 18th, 2011 and therefore is rather obsolete. The game has been updated considerably since then, I just can't be bothered to change my OP.
I was linked to this fun little alpha of a NASA-Spore inspired game by Swadius over in free games. It's called
Kerbal Space Program, here's their website and
the forums. Unfortunately, they have a somewhat weak server running those so heavy traffic puts them down occasionally.
Right now, it's a free alpha and therefore pretty simplistic. You build a rocket, you attempt to launch into space, probably fail. However, designing
idiotic unique rockets and attempting to fly them around while keeping your emotional astronauts alive is quite entertaining.
Screenshots courtesy of Swadius and Tralfaz.
Have a video or two.
Dev video showing some upcoming changes.
Random User video showing him trying new rocket designs. A tiny bit boring but it shows both designing and launching.
It's also quite moddable and they intend to keep it that way, adding new parts for shuttles is incredibly easy. I made some orky bits in about two minutes. Editing textures is easy enough with my ancient version of photoshop, the part cfg text files are well commented and the model is pretty simple as well.
As for payment plan, it's going to be free demos for a little while longer, then they'll be taking the comfortable Minecraft route, start cheap and raise the price as they approach a full release.
Edit ; As for modding, here's the
Projects and Releases board for those of you who need more variety in your shuttle building! I even have a
mod there. There's also the
full modding board if you need help or even more parts that haven't been moved / finished enough to be moved.