Physics Libraries

Physics Abstraction Layer

Open source, free for commercial use. Can select which engine you would like to use from ode, newton, physx, tokamak, true axis, bullet, jiglib, and open tissue. PAL Homepage

Basic Tutorial

Newton Game Dynamics

New Tutorials at Irrlicht Engine Wiki
Old Tutorial at Irrlicht Homepage

Newton Game Dynamics Homepage

Wrappers:

Ode - Open Dynamics Engine

Open Source Physics engine
BSD or LGPL licence

Tutorial at Irrlicht Homepage

Ode Homepage, SourceForge project page

Wrappers:

Tokamak

Tokamak Physics Engine is now released as Open Source Software under the BSD license.

Tutorial at Irrlicht Homepage

Tokamak Homepage

True Axis

Free to use for non commercial.

True Axis Homepage

Tutorial at http://groups.google.com/group/mur_games by Jsmurthy4

PhysX by nvidia

Tutorial at Irrlicht Homepage

PhysX Homepage

Wrappers:

Bullet

Free for commercial use, including PlayStation 3, Open Source multiplatform C++ under the Zlib License.

Bullet Homepage

Wrappers:

Box2D

Quote from the website:
"Box2D is an open source physics engine written primarily for games. As the name suggests, Box2D is a purely 2D engine. Box2D can now handle convex polygons and other shapes coming soon. Box2D falls under the permissive zlib License."

Box2D Homepage