Old AGEIA Physics SDK and runtime
Later was declared Free to use by AGEIA, unsure of the license, but should be open source (consult with your lawyer)
Despite being a hardware company, this is mostly a rigid body dynamics simulator that runs on the CPU
Runtime will need: PhysX_2.6.4_SDK_Core\Bin\win32
PhysXLoader.dll
NxExtensions.dll
NxCooking.dll
NxCharacter.dll
Link Time will need PhysX_2.6.4_SDK_Core\SDKs\lib\win32
NxCharacter.lib
NxCooking.lib
NxExtensions.lib
PhysXLoader.lib
Include will need (depending on features used)
PhysX_2.6.4_SDK_Core\SDKs\Cooking\include
PhysX_2.6.4_SDK_Core\SDKs\Foundation\include
PhysX_2.6.4_SDK_Core\SDKs\Framework\include
PhysX_2.6.4_SDK_Core\SDKs\NxCharacter\include
PhysX_2.6.4_SDK_Core\SDKs\NxExtensions\include
PhysX_2.6.4_SDK_Core\SDKs\Physics\include
PhysX_2.6.4_SDK_Core\SDKs\PhysXLoader\include
Think you will be stuck with 32 bit windows unless you update to a newer version. But this is simple to use if you just need a physics simulation done quick.