I was horsing around in a solar system simulator, out by one of Uranus's moons. I threw a raggedy old tennis ball towards Uranus, knowing that it me throwing it wouldn't actually change its orbit very much. Then I went to follow it and found it orbiting a point in space. "Oh, I guess it got stuck at the lagrange point" I figured.

(In the dream I was calling the gas giant "Jupiter" and the small rocky moon was "Uranus", but that makes no sense, so for the above paragraph I adjusted the names to reflect where I 'actually was').

This solar system simulator was closely linked with a planetary RTS game in which you had to raise rooms full of 'engineers' in order to expand, and the game engine in which they were both written. Things made with this game engine seemed to generally look sort of flat and cartooney, but I got the impression that it was a well-designed engine that abstracted away all the rendering API gunk.