Anyone seen
Gravit?
Just stumbled across it and downloaded it. Looks like it could be very pretty -- certainly inspires me to make the simulator look flashier. (Ooooh, neon!) They also have a lot of features that you all have mentioned. Things like colors based on velocity.
Couldn't quite get it to work right, I don't think. The interface was very confusing, and I tend not to have patience for that kinda thing. Hence why my simulator is so straightforward: "Ooh a planet button, I'll click it! Now I'm adding planets!!" They're all: "Press F6 to start recording" Huh?
Seems they're also more focused on presets with massive amounts of particles. Galaxies, really. And not so much on the 'make your own solar system' thing. But I might be missing something.
Worth a look, though (and free, at that). Lessons learned here: space can be very pretty... and make sure a user can dive right in.