I'm putting together a game that will be played mostly with three dimensional gravity.

By that I mean multiple planets/stars/moons behaving realistically, and path plotting and path prediction in the gravity field.

I have looked at a variety of physics engines, such as Bullet, tokamak or Newton, but none of them seem to be suitable, as I'd essentially have to re-write the gravity engine in their framework.

Do you know of a physics engine that is capable of dealing with multiple bodies all attracted to one another?

I don't need scenegraph management, or rendering, just core physics. (collision detection would be a bonus, as would rigid body dynamics).

My background is in physics, so I would be able to write an engine that uses Verlet integration or RK4 (or even Euler integration, if I had to) but I'd much rather adapt an off the shelf solution.

[edit]: There are some great resources for physics simulation of n-body problems online, and on stackoverflow