Are you thinking of Physijs [0], which is made to work well with ThreeJS? Its a wrapper around Ammojs for ThreeJS.
It does look good and integrates well, but to be honest ThreeJS is so mature and battle tested with multiple renderers (canvas, webgl etc) that when building a physics engine, I really think it would be better to spend ones dev time on the physics and not waste* time reimplementing a portion of ThreeJS.
It does look good and integrates well, but to be honest ThreeJS is so mature and battle tested with multiple renderers (canvas, webgl etc) that when building a physics engine, I really think it would be better to spend ones dev time on the physics and not waste* time reimplementing a portion of ThreeJS.
[0]: http://chandlerprall.github.io/Physijs/
*Obviously not actually 'wasted' time, hacking is great even just for the sake of it - but I'm sure you know what I mean.