What's XUL/XAML?
Your screenshot doesn't impress me at all.
I linked to XULPlanet.com for a reason.
The XML User Interface Language (XUL) is a markup language for describing user interfaces. With XUL you can create rich, sophisticated cross-platform web applications easily.
Whenever I heard about it first, I thought "cool, useful for web-apps". Then I learned that Firefox itself sf an XUL app. I'm looking at the sources now - it's all Javascript, CSS, and XUL (XML) (only for the graphical stuff, and stuff releated to the interface. The rest is C and C++. You don't need to download the source code to see the Javascript, CSS, and XUL. Find browser.jar (for me it's in /usr/lib/firefox-1.6a1/chrome), extract it (it's a zip file - I used unzip), and look in browser.xul, etc.)!
The XUL-ness is what brang along the whole extension infrastructure. Extensions are XUL-built too, they register themselves with Firefox and the XML, etc. is merged into the Firefox XUL.
If I built some web-app in XUL, I could use buttons, menus, etc., kinda like GTK+, etc., and in Windows XP it'd look like an XP app, and on my system it'd look like Firefox does. A native app. But it'd be hosted remotely - you could visit
http://piratepenguins_site.whatever/XUL/app.xul from any XUL browser (only Firefox ATM). If you run firefox with: 'firefox -chrome
http://piratepenguins_site.whatever/XUL/app.xul' it'd run the app not inside a Firefox tab.
Jesus I should've just linked you to
this.