Croquet "players",

If the you are still looking for a physics engine for Croquet this one might 
meet your needs: 
 
Open Dynamics Engine 
http://q12.org/ode/ode.html 
 
"ODE is a free, industrial quality library for simulating articulated rigid 
body dynamics - for example ground vehicles, legged creatures, and moving 
objects in VR environments. It is fast, flexible, robust and platform 
independent, with advanced joints, contact with friction, and built-in 
collision detection." 

ODE is the Blender Foundation’s first choice among physics engines for Blender.
http://www.blender.org 
Blender Conference 2002 proceedings
http://www.blender.org/modules/bc2002/index.html

("Blender is the first and only fully integrated 3D creation suite allowing 
modeling, animation, rendering, post-production, interactive creation and 
playback with cross-platform compatibility - all in one tidy, easily 
downloadable package. Now Blender is Open Source.")
___ 
 
Also, 
Are there any plans to add Open CYC - Common Sense Engine capabilities to 
Croquet? 
http://www.opencyc.org/ 
I imagine such capabilities would be a boon for the educational side of your 
goals for Croquet. 

Cheers,
Darius