Here have already mentioned the Spaceengine project. It seems that they released a new version http://en.spaceengine.org/news/spaceengine_0_9_7_1_released/2013-12-26-8 and went to Steam Greenlight http://steamcommunity.com/sharedfiles/filedetails/?id=214258536.
Nice Aurora Borealis. I don’t think I’ve seen that in any other engine.
What I find most interesting about it is its implementation of gravitational lensing.
Good. Don’t post a new topic.