Free GUI Libraries

It aims to provide a fast, stable, and cross-operating-system graphics user interface (GUI) support system, which is especially fit for real-time embedded systems based-on Linux/uClinux, eCos, and other traditional RTOSes, such as VxWorks, ThreadX, uC/OS-II, and Nucleus. Released under the GPL. he open source versions of MiniGUI are licensed under the GPL license

A cross-platform application framework, Qt is available under GPL v3, LGPL v2 and a commercial license. Now supports Symbian, Android and BB10.

A multi-platform toolkit for building graphical user interfaces. It offers APIs in three basic languages: C, Lua and LED.

FOX is a C++ based Toolkit for developing Graphical User Interfaces easily and effectively.

FLTK is a cross-platform C++ GUI toolkit for UNIX/Linux (X11), Microsoft Windows?, and MacOS X

wxWidgets is a C++ library that lets developers create applications for Windows, OS X, Linux and UNIX on 32-bit and 64-bit architectures as well as several mobile platforms including Windows Mobile, iPhone SDK and embedded GTK+. It has popular language bindings for Python, Perl, Ruby and many other languages.

Windows Template Library (WTL)
Windows Template Library (WTL) is a C++ library for developing Windows applications and UI components. It extends ATL (Active Template Library) and provides a set of classes for controls, dialogs, frame windows, GDI objects, and more.

The Nano-X Window System
Formerly Microwindows, this is an Open Source project aimed at bringing the features of modern graphical windowing environments to smaller devices and platforms.

A complete Ada95 graphical toolkit

Windows++ is a lightweight C++ application framework that lets you program Windows in C++.

A freely available source code distribution for the Motif user interface component toolkit.

LessTif is a free (LGPL) clone of Motif. It is a set of widgets for developing graphical user interfaces

BSD Licensed C++ GUI Library built on top of Windows API but still Linux/xNix support through use of WineLib. Also support for building Pocket PC and Windows CE based applications...

Graphics Vision
Graphics Vision is a graphical Turbo-Vision replacement library for Borland Pascal, targetting to DOS/DPMI and Windows. Rudimentary Free Pascal/Linux support also available.

V C++ GUI Framework
V is a free portable C++ GUI Framework intended to develop a wide variety of applications on different graphical interface platforms.

The xclass library is a C++ GUI toolkit for the X windows environment. It is Xlib-based and consists of a set of components, ranging from simple widgets to complex ones, including also many of the commonly used dialog boxes. The components have the MS Windows-95/98 look and feel.