ParaGUI is a cross-platform high-level application framework and GUI
(graphical user interface) library. It can be compiled on various platforms.

ParaGUI's cross-platform nature is completely based on the Simple DirectMedia
Layer (SDL).

Highlights of the library:

   - published under LGPL 
   - straight forward C++ class-design (see the API documentation) 
   - XML configuration of the new style engine 
   - asynchronous messagehandling (messageposts between objects) 
   - multithreaded 
   - highly customizable widgets (background gradients, background images,
     transparency, colors, fonts) 
   - many standard widgets already implemented (buttons, labels, scrollbars,
     progressbars, windows ...) 
   - create your own widgets (subclass an existing widget)

WWW: http://www.bms-austria.com/projects/paragui/