CEGUI - windowing and widget library

Crazy Eddie's GUI System is a free library providing windowing 
and widgets for graphics APIs / engines where such functionality
is not natively available or is severely lacking. The library is 
object oriented, written in C++, and targeted at game developers 
who should be spending their time creating great games, not 
building GUI sub-systems!

The configure script for CEGUI will detect whether or not you have 
an optional dependency installed and will enable/disable the option 
accordingly.  However, you may want to specify this yourself.  In 
particular, pay attention to the image codecs because you might want 
to disable the others to ensure that the one you want to use is the 
default codec.

Optional dependencies include xerces-c, FreeImage, and DevIL.
There are perhaps others - see output of "configure --help"