The Box2D physics engine was developed by Erin Catto (visit http://www.gphysics.com for further information), who works for Blizzard Entertainment, built the library for a physics tutorial at GDC back in March 2006. It appears that the library was publicly released in Sept 2007, and a version 2.0 landed in March 2008. The 2.1 release from April 2010 included some sweeping changes. The lastest version of Box2D, 2.2, was just released in August 2011, and included performance improvements for large worlds, new joint types like wheel and rope, and many bug fixes (see the release notes).
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