Over the past few days, I've been playing with some of the early fruit of the delivery of Apple's Webkit (which shipped along with Safari (or Ghetto Safari, as Kent prefers.) I'm sure there are others, but the first couple of WebKit-enabled apps I've played with are Steven Frank's WebDesktop 2.0 and YetAnotherAggregator, Shrook.
WebDesktop falls into the "cute toy" category, and that's not a slight against it. The initial version of it was coded basically on a dare, and it worked (as do a number of other OSX apps that need to display rudimentary HTML) by embedding the craptacular HTML renderer built into Apple Help Manager. That renderer was basically designed for simple text and graphics display, so it didn't support CSS, or even right-aligning images, among other things. But then, it's silly to denigrate something for failing to do something it was never meant to do.
Shrook is a three-paned news aggregator, similar to NetNewsWire Lite, with a few novel ideas, like support for historical feeds and nested categories. The current (as of this writing) prerelease version of it uses WebKit for its HTML display, whereas earlier versions used the Apple Help renderer. This allows you to do neat things like being able to view the actual post for an RSS entry, great for feeds that only (big grumble) provide titles or (semi-grumble) short summaries. One feature that would be really nice would be an option to open these full HTML views by default for some title-only feeds (for example, Freshmeat's) on an individual feed basis, so you're not constantly toggling the feature on and off.
Brent Simmons has promised Webkit support soon in an upcoming Netnewswire release, and has been posting progress reports and screenshots on his weblog.
What I'm really looking forward to, though, is the next generation of apps, when people get past the obvious applications of a systemwide fast, lightweight, and correct rendering engine and start to get really creative. I can't wait to see what people come up with.
I can hire one half of the working class to kill the other half.
— Jay Gould