More on declarative UIs and XML for GUI Markup
A good article discussing the various specs “competing” with XAML up at WebStandards.
For more comparisons of XML GUI languages, see DonXML's comparison of XAML and SVG-RCC, and Neil Deakin's point-by-point comparison of XAML and XUL.
The three XML GUI languages above represent only a fraction of those available. Others include XWT, Java GUI Builder, Glade for the GTK+ toolkit used in the GNOME desktop, XML GUI Builder for the KDE Desktop, Laszlo Systems' XML-and-ECMAScript Flash authoring software, Macromedia's Royale Initiative and Kinesis Software's Kinetic Fusion, a Java application that converts Rich Vector Markup Languag, Kinesis' own XML-based vector graphics format, into SVG or Flash and back. [WebStandards.org]