A quadtree terrain with a physics bounds generator. Press mouse 1 to paint terrain and mouse 2 to spawn balls (they spawn in physics sleep mode).
This was a project I did to understand other functionalities a quadtree can provide. When I was young I played a lof of worms armageddon and I was fascinated with their terrain system. I couldn´t understand how you could have something solid that reacts to gameplay and still modify it. Because of that I wanted to try to create my own system as soon as I was knowledgeable enough.
The project source code is available here. It is a bit old but it still works (with exception to the keyboard detection). It uses GWT and java. I know, GWT seems to be dead.