For those not in the loop, Katamari Damacy is a videogame that asks you to roll a ball around a scene, picking up objects that will stick to it and make it bigger. In this online version, what you'll be picking up are all the elements of the webpage in question.
To start the game you just need to drag the Katamari! link to your favorites bar, and click on it when you're on a webpage in which you'd like to play.
Katamari Hack is a fun, curious diversion that will give you some funny moments, and with a good soundtrack to boot.