This is way old, but still pretty awesome. A Finnish grad student spent 5 days making this funny little video game, and it ended up winning the Independent Game Festival this year, an important (I assume) video game contest consisting of many more slickly produced games. Essentially the idea is simply to solve puzzles in a 2D environment where you create shapes subject to-- wait for it-- the laws of physics. That is basically it, just some classical mechanics and the appearance of very rudimentary design. Slate's article on CPD is a good read, and it is especially cool to hear that such a simple and modestly designed game emerged as the talk of the Game Developer's conference (another important thing I assume), despite the many other high profile games showcased there.
Crayon Physics Delux (original non-slick version can be downloaded here for free)