http://code.google.com/p/bullet/ a 3D Physics engine (Zlib license) C++

http://love2d.org/home A lua 2D game engine with Box2D physics engine bindings

http://www.box2d.org/ a C++ 2D physics engine

http://code.google.com/p/isolate/

This utility, isolate, runs processes in a chroot-ed environment, with constrained resource limits, as a random UID, and with limited access to the X server. An isolated program ("isolatee") no longer has all the authority of your user account, but you can still enjoy its legitimate functionality. You can play even maliciously-crafted songs in an unsafely implemented music player, with greatly minimized risk to your other data.