Armadillo Run

Armadillo Run is a physics-based game in which you have to build a Rube Goldberg style contraption to make it to the next level. For each challenge, you're given a budget to buy rope, cloth, metal bars, metal sheet, and other components. Then you have to assemble a structure and adjust the tension of the component so that it will successfully deliver a basketball to a circular blue portal. The challenges get harder as you progress. The game cost $20, but you can download a 10-level demo version for free. (It's for Windows only.)