What are the Open Source alternatives to WPF/XAML? [closed]

Qt is developing QML, which looks a lot like XAML except in JSON. It’s available as a preview built against the current version, and is available in snapshots of the next version.

Here’s a little snippet from http://doc.qt.nokia.com/4.7-snapshot/declarative-ui-components-progressbar.html

import Qt 4.7
import "content"

Rectangle {
   id: main

    width: 600; height: 405
    color: "#edecec"

    Flickable {
       anchors.fill: parent
       contentHeight: column.height + 20

       Column {
           id: column
           x: 10; y: 10
           spacing: 10

           Repeater {
               model: 25

               ProgressBar {
                 property int r: Math.floor(Math.random() * 5000 + 1000)
                 width: main.width - 20

                 NumberAnimation on value { duration: r; from: 0; to: 100; loops: Animation.Infinite }
                 ColorAnimation on color { duration: r; from: "lightsteelblue"; to: "thistle"; loops: Animation.Infinite }
                 ColorAnimation on secondColor { duration: r; from: "steelblue"; to: "#CD96CD"; loops: Animation.Infinite }
               }
           }
       }
   }
}