From CEGUI Wiki - Crazy Eddie's Gui System for Games (Open Source)
For a more up-to-date list go to http://cegui.org.uk/features
CEGUI's main features are:
- Mature codebase, CEGUI has been around since 2003!
- Multi-platform support - Windows, Linux and Mac OS projects/solutions are available
- Support for both 32bit and 64bit architectures
- Heavily data-driven by using XML files, a generic property system and powerful skinning abilities
- Very flexible, you can code your own widget renderers, use your chosen XML parser, script module, etc...
- UNICODE support - utf8 and utf32 (check the Fonts sample)
- Renderers for OpenGL, DirectX 9, DirectX 10, DirectX 11, Irrlicht, Ogre3D, Crystal Space (provided by the Crystal Space team) and Open Scene Graph (provided by the Open Scene Graph team), DirectFB (experimental). A null renderer is provided as well.
- Clear interface in case you want to write your own renderer
- Several tools, including a Layout- and Imageset editors
- Many wiki pages and useful sample projects
- Commercial products have been developed with CEGUI already. Check the Projects Using CEGUI.