QuickBox2D: AS3 physics engine
The first time I saw a really convincing physics engine working on a PC game was during a Half Life 2 session. All that Havok physics created an unique game experience. Luckily the use of physics inside games has grown and now we have a wide range of tool to use, even in Flash games.
QuickBox2D is one of them. It is a mini-library created to work with Box2DFlashAS3, which is an AS3 port of the famous Box2D C++ physics engine. The main purpose of this library is to significantly simplify instantiation of rigid bodies and provide a simple way to bind them with custom graphics.
You can start with QuickBox2D by reading this great kick off tutorial. It explains the engine itself and demonstrate how to use some of it’s features.