I'm looking for a physics engine to use in an XNA project (2D or 3D). Because it's for XNA, it needs to fulfill some requirements:

1. Not necessarily free, but close to it is obviously preferred
2. Managed code only (or it won't run on the 360)

For 3D I know of

• BulletX (It works, and I'm using it now, but it's not active and could use more work)

For 2D I know of

• Velcro Physics