Crazy Eddie's GUI (debugging libraries)

 CEGUI is a free library providing windowing and widgets for graphics
 APIs and engines where such functionality is not natively available
 or is severely lacking. The library is written in C++, is object
 oriented, and is primarily targeted at games developers who should be
 spending their time creating great games, not building GUI sub-systems
 .
 This version of CEGUI natively supports the OpenGL rendering target
 and provides debugging libraries for it.