Demos of ODE with Squeak and Croquet impressed me a lot. ODE is a high performance library for simulating rigid body dynamics. You see ODE in action in a demo video of Croquet about minute 58.

Takashi Yamamiya designed an ODE plugin and etoy interface for Squeak.
A link to the vm plugin for PowerPC Macs by Dominique Dutoit can be found on the same page page.

I just build the vm-plugin for Intel Macs based on Takashi's work. Here are the steps for building the vm plugin for Mac OS X 10.4.7, Sqeuak VM 3.8.12betaU, 3.8-6665 image with Xcode 2.3 (see also a japanese guide):

1) ODE Library:

• download, compile and install ODE 0.6 Library or download the pre-compiled library:

2) Generate Plugin Sources:

• get the current Squeak vm sources
• open a new image (I used 3.8-6665)
• open the SqueakMap Package Loader and install package ODECo 0.2
• open the VMMaker, set path to platform code and the path to the generated sources
• select ODEPlugin as External Plugin and generate it

3) Build Plugin with Xcode:

• create a new Xcode project: Carbon Bundle
• insert a reference to ODEPlugin.c
• insert the references to the header files of the vm (see also PrintJobPlugin)
• • /Developer/SDKs/MacOSX10.4u.sdk/usr/include/i386/types.h
  • platforms/Mac OS/vm/Developer/interp.h
  • platforms/Mac OS/vm/sqConfig.h (comment out statment #include <mactypes.h>)
  • platforms/Mac OS/vm/sqNamedPrims.h
  • platforms/Mac OS/vm/sqPlatformSpecific.h
  • platforms/Mac OS/vm/config.h
  • platforms/Cross/vm/sq.h
  • platforms/Cross/vm/sqMemoryAccess.h
  • platforms/Cross/vm/sqVirtualMachine.h
• add libode.a (/usr/local/lib) as existing library to the xcode project
• adjust configuration for release build target
• • set Architectures to i386
  • set Header Search Paths to /usr/local/include
  • set Other Linker Flags to -lstdc++
  • check 'Force Package Info Generation'

You also might download the pre-built ODEPlugin for Intel based Macs:

Please note that I am not involved in any means in the development of ODE and ODECo. Therefore I can not help with any bugs