Found this cool online tool that lets you create, simulate, and visualize custom solar systems.

[Infinite_Spaces.]

Also lets you save the systems localy, and exports to various formats including obj, seems pretty in depth and is great fun to play with.

Check it out here: AstroLight™

 

[TROPtastic]

Neat visualization. It would be nice if it had an N-body solver in the simulation, rather than restricting the planets to stable orbits (whether realistic or not).

I found this javascript Orrery tool that runs orbital interactions, but it doesn't allow customization of solar systems in the front-end. Maybe someone would be interested in modifying the code.