cross platform widget tookits

GTK

http://www.gtk.org

Win32, X11

C

gtkglarea and gtkglext for OpenGL.

Already working with cmgui on win32 and linux

wxwidgets

http://www.wxwidgets.org/

Win32, Mac OS X, GTK+, X11, Motif, WinCE, and more

C++, Python, Perl, and C#/.NET

wxGLCanvas for OpenGL from V2.1.14

The wxWindows Licence is essentially the L-GPL (Library General Public Licence), with an exception stating that derived works in binary form may be distributed on the user's own terms. This is a solution that satisfies those who wish to produce GPL'ed software using wxWidgets, and also those producing proprietary software.

XML resource files, some third party GUI builders, Native look and feel

FLTK Fast Light Toolkit

http://www.fltk.org/

UNIX/Linux(X11), Microsoft Windows, and MacOS X

C++

OpenGL support

FLTK is provided under the terms of the GNU Library Public License, Version 2 with exceptions that allow for static linking.

GUI builder FLUID

Fox Toolkit

http://www.fox-toolkit.org/

Linux and Win32, Requires X11 for OSX

C++

LGPL 2.1, Aims for identical look and feel.

GLGOOEY

http://glgooey.sourceforge.net/

OpenGL

XUL

http://www.xulplanet.com/

Linux, Win32 and OSX

XML, Javascript and C++

Mozilla Public License

Mozilla toolkit for creating applications. We are using this for mozCmgui.