quuz is to quux what baz is to bar. In other words: Nothing much at all. This lovely domain was registered with the intent to create a playground for projects which do not really fit anywhere else. I would have put them on annevankesteren.nl if the hosting conditions for that domain were better at that time, however, moving things over is not an option anymore given that cool URIs don't change. After all, quuz.org is pretty cool. And above all, short.
quuz can also be seen as a mistyped metasyntactic variable of which the correct spelling is quux. However, this is a much less interesting point of view and is therefore strongly discouraged.
quuz first ever hosted playground, is the XML5 playground which allows people to see how XML5 will deal with their markup.
quuz second playground is on anolis.quuz.org, aptly named Anolis ALPHABETA. A Web service that generates cool specifications from simple input.