Chipmunk2D is a 2-dimensional real-time rigid body physics engine written by Scott Lembcke that is designed to be portable, lightweight, fast, and easy to use. Prior to version 7, two main versions of the library existed. Chipmunk2D Free was written purely in C99, and freely available under the terms of the MIT License. Chipmunk2D Pro was a proprietary upgrade designed for development on mobile devices.