QUOTE
WebKit is an open source web browser engine. WebKit is also the name of the Mac OS X system framework version of the engine that's used by Safari, Dashboard, Mail, and many other OS X applications. WebKit's HTML and JavaScript code began as a branch of the KHTML and KJS libraries from KDE. This website is also the home of S60's S60 WebKit development.
It's the engine around which Safari is built. When you download it, and start it up, it looks like Safari - because it actually is, just with the newest Webkit engine. When you start up Webkit, you'll have all your usual Safari bookmarks and preferences (but cannot use extensions). Think of it as trading out the engine on your car - looks the same from the outside, but under the hood, it's the latest model. This analogy isn't quite accurate though - because you still have the old car (Safari) with the old engine - and you can even run it at the same time. But things like preferences and bookmarks are shared - add a bookmark to Safari and it will immediately show up in Webkit. And yes, if you're running both at the same time, it can be confusing, since they LOOK identical - except if you click on "About Safari" - you will see the Webkit build revision number there.
How different the two seem depends on where Apple are with the Safari release schedule; right now, there doesn't seem to be a huge difference to me. BTW - it's very stable and I have no problems with it as my everyday browser.
