Kerbal Space Program:
http://kerbalspaceprogram.com/Single player, can be per-ordered for $18 which gives access to the newest version, otherwise there's a demo version (which is a much earlier version).
It's a space simulator, allows you to build rockets and taking them into orbit (everything manually, though, offers some visual support).
atm it's in early alpha stage, so it's quite lacking, but nonetheless fun.
I made a
Space Station and later on "docked" (though, it doesn't support real docking yet, so I had to use landing gear as a "claw).
(full res:
http://i.imgur.com/wiaXB.jpg)
