Someone suggested that it might be useful to have a sticky list of physics engines and reference material available here (for convenience...the info is all available elsewhere). So, I am giving it a try.This thread is not for discussions. It is simply meant to contain links to commonly-requested information. I'll leave the thread open for contributions, but I will remove anything that is remotely off topic or tangential. Add links, but do not discuss!
-------------------------------------------------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

[grhodes_at_work note] - I migrated most of the links over to the top article in the thread. I left one below, since there is currently no link to code.
I also left some unaddressed suggestions, for a future reminder.
[end note]

And maybe also some of the XNA ports:

Tokamak though this doesn't look like it's publicly available yet.

I also suggest noting on each:

- What language it's in

- What platforms it supports

And maybe if you update the original post then this one can be deleted?

[Edited by - grhodes_at_work on December 18, 2007 11:30:38 AM]

For completeness I would also add the work of Jacobsen and Muller:

And the Baraff Siggraph notes and his other publications:

Also I find these four books and their associated websites useful:

Also add Open Tissue to the list of engines and add Erin Catto's GDC presentations and not only Box2D.

[grhodes_at_work - added links to Open Tissue and Erin's personal blog page to the top post. Catto's presentations are on the Essential Math site]

[grhodes_at_work second edit - moved Jacobsen, Muller, Baraff, Ericson, v.d. Bergen, and Eberly links to the main post. Removed links from here to avoid confusion with duplicates.]

[Edited by - grhodes_at_work on September 8, 2009 10:55:03 AM]

And Tokamak is indeed open source here:

[grhodes_at_work edit. Made sure these links were in main post, and removed links from here to avoid confusion with duplicate links]


[Edited by - grhodes_at_work on September 8, 2009 10:58:10 AM]

Benchmarks/copmarisons:
Physics abstraction layer interactive benchmark graphs (to help you choose the most appropriate physics engine)
Evaluation of real-time physics simulation systems (contains a matrix comparison of the features of 7 different engines)
Evaluation of Physics Engines and Implementation of a Physics Module in a 3d-Authoring Tool

Physics content creation:
Scythe physics editor

Articles/Resources:
Adrian Boeing's physics engine list
Wikipedia Physics Engine article
Racing car physics
Chris Hecker's Rigid body tutorials
Roy Featherstone's publications (see the excellent overview paper: Robot Dynamics: Equations and Algorithms. IEEE Int. Conf. Robotics & Automation, pp. 826-834, 2000.)
Gaffer on game physics
Flight gear, aerodynamics
SSS, aerodynamics

More Engines:
see Adrian Boeing's physics engine list, eg:
Dynamechs

Notes:
-OPAL is no longer being developed (ie:dead)
-Tokamak is publicly available, and open source, see tokamak downloads

Technical references:
Eran Guendelman's homepage
Impulse-Based Dynamic Simulation of Rigid Body Systems

Perhaps add Carbon to the list? Looks rather nice...

Also BEPUphysics

physx is under very active development, so it's not dead

physx is under very active development, so it's not dead

Indeed - that's just a formatting error - Oxford Dynamics is supposed to be on a new line.

It's probably worth linking to http://iphys.wordpress.com/2012/02/28/interactive-simulation-of-rigid-body-dynamics-in-computer-graphics/ "Interactive Simulation of Rigid Body Dynamics in Computer Graphics" by Jan Bender, Kenny Erleben, Jeff Trinkle, and Erwin Coumans as it's a very recent summary of pretty much everything.