http://krypton.codeplex.com
Krypton allows users of the XNA framework to easily add 2D lighting to their games. Krypton is fast, as it utilizes the GPU and uses a vertex shader to compute 2D shadows, relieving additional stress from the CPU to compute more game-like tasks.
Krypton currently supports simple softshadows and occlusion (For convex objects).
The source can be found on http://krypton.codeplex.com/
The only functionality included in the source is the code Krypton light engine. The Box2D physics are not included.