Havok (software)
From Halopedia, the Halo wiki
The HAVOK Physics is a physics engine developed by Irish company Havok and has been used by a large number of projects, both in the video game and movie industries, by using dynamic simulation to simulate physical interactions realistically, including such features as ragdoll physics or intelligence in massive falling objects.
HAVOK in Halo titles
Trivia
Halo: Combat Evolved is the only Halo title that utilises Bungie's in-house physics engine.