A classic puzzle game adapted for the web. If you enjoy it, click through on the source link, or search on the game's author for more of his examples.
Some of the other cool features of this script are that it keeps track of the number of moves and seconds elapsed. It also lets you choose the number of squares and reflows the board using some classic DHTML techniques. All in all, this is a very cool example, and an engaging game (if you enjoy puzzle games.)
That said... enjoy. To start the game, either select a new level and press "Go" or click on any of the board pieces to shuffle them and start the game.