Coherent UI is high-performance multi-platform user interface system for game developers and studios.
Fast UI toolkit for hardware accelerated games & applications
GUI Without Extravagant Nonsense
Crazy Eddie's GUI System
Awesomium makes it easy to use HTML UI in your C++ or .NET app
AntTweakBar is a small and easy-to-use C/C++ library that allows programmers to quickly add a light and intuitive graphical user interface into graphic applications based on Open...
GiGi (aka GG) is a GUI library for OpenGL.