If you're real keen, you can check out a really old sample version of George, circa 2001, before I even added 3D hardware support.
Just download this zip file, unzip it, run the exe, and choose file->open to check out one of the 2 sample scenarios. Check the readme.txt file for key controls.
The most recent version is OpenGL and all kinds of flakey, (+ it relies on bunches of large textures) so I am not posting it at this time.
George is an old pet project I started around 2000 [!] and come back to from time to time. It's kind of broken at the moment, and it will probably never be completed, but next cycle [should there be one] I might try to release a version for people to play with.
My intention was to create a generic extensible simulator capable of simulations with scales ranging from the minute (millimetres) to the enormous (light years). Modelling physical interactions is not a simple task [relativity doesn't even get a look-in], and keeping up with latest 3D rendering technologies is a full-time job in itself, so George may never see the light of day :(
There are a couple of more serious [and finished] astronomical simulators out there, so if you're interested, you might want to check out:
Click on the thumbnails below to see higher resolution screen shots, mostly from realtime renderings (except for the high detail asteroid ones, which can take up to several seconds).