2D physics engines are the things that are used to create games such as Angry Birds, Where’s My Water? and others. With a 2D physics engine you define the objects, the “physics” and how things interact. The engine takes care of the rest!
The demo project displays a cart at the top of the screen which you can move around with the left and right arrow keys. The car will push and interact with the other objects on the screen. You can see here that I got my cart stuck under a block:
It seems like some fun games could be created with this and best of all the engine is free with full source code!