Havok Physics is a commercial physics engine, a programming library to add physics functionality to a game for example. It can be used with C or C++ and works on Windows, Xbox, Xbox 360, GameCube, Wii, PlayStation 2, PlayStation 3, PSP, Mac OS X, and Linux.
Havok has been used in several commercial game titles like Bioshock or The Elder Scrolls IV: Oblivion.