Built using Microsoft's XNA, it's designed to only work with a gamepad of some nature, and ideally a 360 controller. The game is an attempt to create a reasonably accurate physics model of a human gymnast, albeit one built of rectangles, teaching you to spin, flip, grab and leap about the horizontal bars. It then gets extremely silly, flipping you from boingy poles down curved corridors of poles, challenging you to master the remarkably complicated controls. Left analogue stick does the top half of the body, right taking care of the legs. And there's a slo-mo mode for mastering the trickiest moments.
The only trouble is, it doesn't seem especially fond of non-360 controllers, and the person with the adapter for the 360 pad moved out of my house a few months back. A couple of controllers were plugged in, but both had the right analogue permanently jammed to the left, which is quite a problem in the dizzying world of gymnastics. However, if you have yourself a 360 pad, or a controller with which it will comply, definitely get yourself a copy. It's completely free, and really rather satisfying to get to grips with. And you can play it on PC now, rather than waiting for the Xbox version.