Box2DFlash is a free 2D physics engine for Flash. It's a popular choice for making games and toys in. Box2DFlash is a 2D rigid body simulation library for games. Programmers can use it in their games to make objects move in believable ways and make the world seem more interactive. From the game's point of view a physics engine is just a system for procedural animation. Rather than paying (or begging) an animator to move your actors around, you can let Sir Isaac Newton do the directing. Box2DFlash is written in AS3, and resides in the Box2d namespace. Most of the types defined in the engine begin with the b2 prefix, to match the C++ version.