Xul. InkFace - altcanvas - Google Code. Inkface is SVG based GUI framework.
You design the GUI in an SVG image editor (like Inkscape/Illustrator) and use inkface framework to wire your program logic with the elements of your SVG GUI. The benefits of this approach: Rich GUIs of any colors and any shapes. Replacing the GUI is as trivial as replacing the old SVG file with new one.