Does anyone know a good orbital mechanics simulator?

[Starwhip]

I need to find a free or at least extremely cheap orbit simulator that can do a main mass (a star) and at a minimum 2 planets. Units of distance from the main star should be in AU's and I need real units, not weirdo cheapo ones that don't really exist. And you should also be able to set the masses of the planets, in either Kg's or in Earth Masses.

[andrewas]

This http://www.orbitsimulator.com/gravity/articles/what.html should do everything you want.

[Starwhip]

Wow. That works great! Thanks!

[Kavaeric]

You can try out The Universe Sandbox, though I'm not exactly sure its physics are 100% NASA-seal-of-approval correct.

You can buy it on Steam or as a standalone http://universesandbox.com/