Yahoo! released the latest version of its UI utilities this week, including the components used in the new Yahoo! homepage design. You can use the various utilities to build your own website, but Dustin Diaz decided to build a version of Tetris.
One of the good things about releasing your code to the world is you never know just how people will use it. I doubt anyone at Yahoo! thought about gaming when they released the UI widgets but developers are resourceful!