Porting would be easy - ActionScript is just a variation of Javascript (both are ECMAScript implementation, to be precise).
I implemented a much simpler version of a 2d physics engine like this in a graphics class back in college (but in gtk on linux). It was really fun to do and surprisingly straightforward. A lot of the math gets much hairier in 3D.
This is really great!
This is really good. There is a small problem though when you move to fast the object that you're holding will go through edges.
Also, the other demos are even better, like the ragdoll. This is very impressive!
Really interesting stuff. I have no idea what I would use this for right now, but have often had thoughts about trying to implement something like this.
This kind of stuff is pretty neat when implemented in games - never seen an example that gave such a real life feeling though! Props!