OS X Software: Konfabulator

More of a development platform than a standalone application, Konfabulator is a rather unusual, yet fun tool that runs skinnable desktop widgets. Not just any widgets, but widgets created by third party developers in a rather unexpected language - JavaScript - a very accessible, relatively easy to learn language with countless users ready to go. The tool also offers a 72 page XML and JavaScript Reference guide (designed very similar to an O'Reilly book) will full documentation about all the prebuilt objects, functions, events, and properties.

So, what can you build with it? That's up to you. But you can check out the already full gallery of widgets, including various clocks, an ebay auction watcher, various RSS XML news readers, an album cover viewer (from what you're listening to in iTunes), a Mail checker, and a few simple games.