Game Gui

Anyone know of a good game gui that uses OpenGL? Specifically I''m looking for one that does not depend on the native windowing system, and is skinnable. Lots of features would be great but something simple is ok too. I would also prefer C++ over C but I''m not picky. I already know of glui, glow, glgooey, and mui but none of these meet my criteria. Either they use that native windowing system, or they are not capable of running alongside another non-gui window, and none of them --as far as I know-- are skinnable. I''ve trying to write my own too, but I figured someone must have done this before. Probably better than I have. So if one is out there that I don''t know of that would be prime.