WebKit
WebKit is Apple's open-source browser rendering engine. It is the best available engine on the market right now.
Usage
WebKit is used for two parts of the application: the InfoWindow? and the QuickPlayWindow?. Each of those is really some XHTML and JavaScript somewhere that is being rendered to the screen in a transparent window. Yes, it's just like Dashboard. No, that's not where I got the idea.
The Framework
WebKit comes pre-packaged on Mac OS X 10.3 and above (I think). Of course, iTC requires 10.4 anyway, so that's convenient. However, the version included on the system is considerably old and is missing support for a great deal of features. For this reason some newer WebKit frameworks are included in the source. Unfortunately, this makes the binary really big, but it's really only for the time being. I am assuming that when 10.5 is released it will have the latest and greatest WebKit installed and we can then ditch the home-rolled frameworks in favor of linking against the system libraries and making the binary smaller. Until such time...

