Box2D is a free open source 2-dimensional physics simulator engine written in C++ by Erin Catto and published under the zlib license. It has been used in Crayon Physics Deluxe, Limbo, Rolando, Fantastic Contraption, Incredibots, Angry Birds, Tiny Wings, Transformice, Happy Wheels, and many online Flash games, as well as iPhone, iPad and Android games using the Cocos2d or Moscrif game engine and Corona framework.