-------------------------------------------------Commercial Physics Engines (usually written in C++)-------------------------------------------------
Note that most of these have license options that are attractively priced for indie and hobby developers.
Havok (3D, free for non-commercial and inexpensive commercial PC games, fee-based for games above a price limit, non-game applications, and consoles. Download available from Try Havok.)
NovodeX (see Ageia PhysX)
Ageia PhysX (previously NovodeX, now NVIDIA PhysX)
NVIDIA PhysX (previously Ageia PhysX) (3D, free for PC-based games, free for PS3 through Sony pre-purchase, fee-based for other consoles)Oxford Dynamics (3D, vehicle sim - appears to be dead...)
Digital Molecular Matter (DMM) from Pixelux Entertainment (3D, fee-based licensing)
SPE Simple Physics Engine (3D, free for noncommercial, fee-based for commercial)
Chrono::Engine (3D, free for noncommercial use, fee-based for commercial)
True Axis (3D, free for noncommercial, fee-based for commercial with a reasonable indie license option)
Gino van den Bergen's SOLID collision detection library (3D, fee-based for commercial, open sourced for GPL/QPL projects)
SimVex - (previously simul-X) Addon library for Havok enabling game-quality vehicle creation of any configuration, cars, motorcycles, aircraft, etc.
CarX - CarX is a car physics engine for AAA racing games. (3D,C++,fee-based licensing)
-------------------------------------------------Open Source and Freeware Physics Engines-------------------------------------------------
Bullet (3D, open source Zlib license)
Open Dynamics Engine (3D, open source BSD license)
Box2D (2D, open source permissive Zlib license)
Tokamak Physics (3D, open source BSD license - Sourceforge Link)
Newton Game Dynamics (3D, custom free-use license)
JigLib (3D, open source Zlib license)
Chipmunk (2D, open source unrestrictive MIT license)
Open Tissue (various, open source Zlib license)
------------------------------------------------------------XNA-Compatible ports------------------------------------------------------------
JigLibX - XNA port of JigLib (previously JiggleX)
Bullet for XNA
------------------------------------------------------------Other ports------------------------------------------------------------
JigLibFlash - port of JigLib to Flash via ActionScript 3
------------------------------------------------------------"Abstraction Layers" that support multiple physics engines------------------------------------------------------------
Open Physics Abstraction Layer - OPAL (is this dead?)
pal
-------------------------------------------------Technical References (most are quite advanced)-------------------------------------------------
Tutorial presentation materials on game physics from GDC (Essential Math) A good starting point for beginners
Kenny Erleben's Ph.D Thesis on Multibody Dynamics Simulation
Article on Sweep-and-Prune collision detection by Pierre Terdiman
Dr. Jan Bender's page on impulse-based dynamics, with papers and a downloadable library
Claude Lacoursière's Ph.D Thesis on multibody dynamics simulation
Advanced Character Physics - Thomas Jakobsen (often referenced)
Position-Based Dynamics by Muller et al
Links to various papers by David Baraff et al
-----------------------------------------------------------Links to other physics directory/resource/wiki/blog sites-----------------------------------------------------------
Hardwire's Game Physics Resources
Erin Catto's Physics Weblog
Christer Ericson's Real-Time Collision Detection website (companion to his book)
David Eberly's Geometric Tools website - home of the Wild Magic game engine as well as numerous technical articles and useful code