Box2d s a free open source 2-dimensional physics simulator engine written in C++ by Erin Catto and published under the zlib license. The engine may be compiled in fixed point and floating point modes, and has been used on the Nintendo DS, Wii, and several mobile phones (including Android and iPhone) as well as most major operating systems. ox2D performs constrained rigid body simulation. It can simulate bodies composed of convex polygons, circles, and edge shapes. Bodies are joined together with joints and acted upon by forces. The engine also applies gravity, friction, and restitution.