We're always excited to see others who are as passionate about simulating reality as we are. I wish them success in their pursuit of a very exciting and challenging problem. We'll add them to a list of other apps on our FAQ.
And to be fair... Universe Sandbox was a clone of other gravity simulators that came years before it, so no need to critique them for that. My interest in gravity simulators started back in middle school when my Dad showed me this very simple gravity simulator with CGA graphics and I've been fascinated ever since. Perhaps Universe Sandbox might be that inspiration for the creator of SciXP/Milky Way.
And the game does run... it's in a rar compressed format. You can use 7-Zip to extract it...
http://www.7-zip.org/