Havok is a physics engine developed by the Irish company with the same name. The "Havok" was designed primarily for video games, and allows for real-time collision and dynamics of rigid bodies in three dimensions.
The engine provides multiple types of dynamic constraints between rigid bodies (e.g. for ragdoll physics), and has a highly optimized collision detection library. By using dynamical simulation, Havok allows for more realistic virtual worlds in games. The company has also released the product Havok Animation, which provides efficient playback and compression of character animations in games, and features such as inverse kinematics.
Havok is the physics engine that was used for L.A. Noire, in addition of a special in-house engine, which includes a combination of facial motion capture and animation software.