Box2D is a 2D physics simulation lib for games made by Erin Catto (box2d.org)
This is a sligthly modified version, for better Monkey2 compatibility.
See modules/box2d/LICENSE.txt for original Box2D License.
Original Box2D uses methods called "Step", which is a Monkey2 Keyword. These Methods have been renamed into "Stepp".
You can see basic examples in modules/box2d/bananas.