If you like physics, or playing with stuff, you'll like this: FantasticContraption
A perfect example of exploring solutions, alternatives and refinements. For those of you who have been on my exploratory testing course, I couldn't teach ET with it, but I urge any readers interested in exploration to watch themselves - or someone else - working towards solutions, general applications, principles, components. I've just lost a chunk of time myself in a gentle whirl of levers and engines. Reminds me of Meccano, but it's fast, flexible, and never runs out of bits (or seizes up with friction). Must get AquaForest back on to the iPod Touch.