Algodoo

This bomb works best when in an area enclosed by planes. The particles temporarily jetison themselves inside the planes, building an extreme potential before their velocity reverses and they launch back into the area. However, the bomb is pretty powerful nonetheless in an unbounded area, but not the most powerful possible for its size. This is as far as I know the most powerful circle-bomb (provided the same number of circles/tracers) for its size for enclosed areas.