Likewise, Kerbal Space Program, which is somewhere between Space Engine and the hardcore space sim Orbiter. It consumed about a month of my life.
If you checked it out when it was first released, I highly recommend (staying away from) its current state - it has matured very well.
This is the monthly thread for posting media of various types that you've found that you enjoy. I find that exposure to LW ideas makes me less likely to enjoy some entertainment media that is otherwise quite popular, and finding media recommended by LWers is a good way to mitigate this. Post what you're reading, listening to, watching, and your opinion of it. Post recommendations to blogs. Post whatever media you feel like discussing! To see previous recommendations, check out the older threads.
Rules: