ODE is an open source, high performance library for simulating rigid body dynamics. It is fully featured, stable, mature and platform independent with an easy to use C/C++ API. It has advanced joint types and integrated collision detection with friction. ODE is useful for simulating vehicles, objects in virtual reality environments and virtual creatures. It is currently used in many computer games, 3D authoring tools and simulation tools.
Used in:
S.T.A.L.K.E.R.: Shadow of Chernobyl
Call Of Juarez
Softimage|XSI
BloodRayne2
Pedal to the metal
...and houndreds more...just for free...
http://ode.org/Russell Smith is the primary author of ODE.