This one seems like a very nice project. I thought I knew all engines but then stumbled upon this.
http://www.spehome.com/
Of course its C++ (I think)…
The demo should work but u have to download the physics dll and put it in the demo folder.
Well, given it is not free for Linux, and the Demo does not work on 64-bit machines, I will simply give up on it. :x