wxWidgets Is a mature GUI toolkit that uses each platform's native API, so provides a native look and feel from one codebase. This makes it more thoroughly cross-platform than
Tk is a graphical user interface toolkit that takes developing desktop applications to a higher level than conventional approaches. Tk is the standard GUI not only for Tcl, but f...
IUP is a multi-platform toolkit for building graphical user interfaces. It offers a simple API in three basic languages: C, Lua and LED. IUP's purpose is to allow a program s...
Open source Python library for rapid development of applications that make use of innovative user interfaces, such as multi-touch apps.
The Clutter Project is based on OpenGL or OpenGL ES which means it can run on anything that supports OpenGL ES. Qt LGPL and other GUI cross platform tool kits are generally limi...
FOX is a C++ based Toolkit for developing Graphical User Interfaces easily and effectively. It offers a wide, and growing, collection of Controls, and provides state of the art f...
NanoGUI is a a minimalistic cross-platform widget library for OpenGL 3.x. It supports automatic layout generation, stateful C++11 lambdas callbacks, a variety of useful widget ty...