I can't tell you of any fully usable GUI for now.
I know one that uses widget hierarchy, one that does not, but none of these is finished.
I can speak a bit of mine.
It's an immediate mode GUI (widgets can't contain sub-widgets) made for a video game I'm developing with some friends of mine but I don't think it's limited to my project.
I'm focusing on three points :
- customizable : the whole GUI design (widgets' background/border color, text color, color when it's enabled/disabled, border width) can be loaded from an XML file
- extendable : you can make your own widgets really easily by subclassing my base Widget class
- easiest use : minimal functions (developer), intuitive interface behaviour (user)
It's obviously portable. For now it depends on libxml2, boost and SFML. I'll drop the libxml2 dependency as soon as I think of it.
What I've done till now : global interface event handling, global interface drawing, focus handling, base widget, text field (insertion, moving with cursor and deletion), button (using boost for target function binding) and simple box. Plus an XML file loader and a Matrix class. What I'm working on : TableView, Label, Checkbox and RadioButton.
Now.. if you wish.. I can give you the current sources. They are mostly not commented.