Is nobody else playing this? It's a nerdy physics simulation in which you build rockets and send your astronauts to various celestial bodies, just because. I have had a ball trying to rescue poor Jebediah from an eternity wandering the cold, lifeless steppes of the Mun.
I haven't had this much fun with a game in a long time. I highly recommend it. Especially for those of you with a casual interest in physics/rocketry. A warning, the learning curve is steep, but there are lots of resources to help you through it.