PhysX creates effects and scene filled with dynamic destruction, particle based fluids, and life-like animation with accurate physics simulation.
Havok is a collision detection and physical stimulation technology for interactive software for digital media creators in games and movie industries.
Bullet is a physics engine which stimulates collision detection, soft and rigid body dynamics, soft body support, and more.
A modular, extendable, and easy-to-use physics engine for javascript
Box2D is an open source C++ engine for simulating bodies in 2D that has features in collision, physics, system, testbed, and documentation.