Phun is a two-dimensional physics sim or a “2D physics sandbox” as its Swedish creator calls it. It allows you to mess around with blocks, levers, and balls and create simple (and complex) machines to accomplish a variety of tasks. It even allows you to tinker with the laws of gravity, friction, viscosity, and just about every other variable you could imagine.
The interface works at many different levels and is appropriate from early primary up to senior high school and beyond. It is a constructivist learning tool; built around the belief that people learn best when they can explore and make a meaningful product of their own choice. Personally, I’ve wasted hours on it already!