Last year we blogged about the availability
of nightly WebKit builds (WebKit being the HTML rendering engine that Apple uses in OS X and has made available to the Open Source community). The Apple Developer Connection has an article
up explaining what nightly builds are and why you might want to use them. The long and the short of it being that if you are a developer using WebKit to power your app (or widget) nightly builds give you a chance to see the changes in WebKit before they become part of the OS.
[via Surfin' Safari