It's very hard for a game developer to strike the right balance between rewardingly difficult and so frustrating as to be unplayable. Pivvot walks a fine line, but manages to be mind-bendingly difficult and still somehow incredibly fun. All you have to do is guide an orb along the track and avoid obstacles by pivoting clockwise and counter-clockwise. Yeah, that doesn't sound challenging, but it really is.
The orb hangs out at the end of a fixed tether, which you can swing in either direction.