Bluestone Consulting (BCI)
   Provide Unix and Java GUI builder tools such as JClass, JProbe, UIM/X, db-UIM/X, XRT and Platinum.
   http://www.bci-bluestone.com/

Droplets
   A rich thin client framework for building software applications that combine the usability and speed of desktop software GUI with the centralized administration and universal accessibility of Web apps.
   http://www.droplets.com/

FOX GUI Toolkit
   A cross-platform C++ based Toolkit for developing GUIs easily and effectively (Unix/X,Win32). [Open source, LGPL]
   http://www.fox-toolkit.org/

GLO GUI Library
   A platform independent graphical user interface library developed specifically for games.
   http://www.thomasandamy.com/projects/GLO/

GNUStep
   An attempt to provide an Object-Oriented application development framework and tool set for use on a wide variety of computer platforms. Based on the original OpenStep specification provided by NeXT, Inc.
   http://www.gnustep.org/

GUI Library Technical Information
   The PEG GUI library home page. PEG is a C++ GUI library designed exclusively for real time embedded systems.
   http://www.swellsoftware.com/

General Graphics Interface (GGI)
   Project that aims to develop a reliable, stable and fast graphics system that works everywhere which will allow any program using GGI to run on any platform requiring at most a recompile.
   http://www.ggi-project.org/

General Interface
   Full windowing and rich client framework written in JavaScript enables full featured application solutions to run in just a standard browser with astoundingly rapid development and deployment ease.
   http://www.geninterface.com

GraphApp
   Toolkit for cross-platform GUI programming on Windows, X-Windows, Linux and Macintosh systems. It works with the C, C++ and Python languages, and the source code can be freely downloaded here.
   http://enchantia.com/software/graphapp/

Imake-Related Software and Documentation
   Imake FAQ, software accompanying the O'Reilly "Software Portability with imake" book, notes on use with Motif and X11, imake-related utilities source code.
   http://www.snake.net/software/imake-stuff/

JX Application Framework
   JX is a full-featured C++ application framework and GUI class library for the X Window System.
   http://www.newplanetsoftware.com/jx/

LGI (Lightweight GUI Library)
   A Lightweight, cross-platform GUI library and application framework. Currently 3 ports exist, Win32, Linux and BeOS. [Open source]
   http://www.memecode.com/lgi.php

LiteClue Widget
   A free bubble or balloon help X Widget.
   http://halibut.compgen.com/widgets/LiteClue.html

ParaGUI
   A cross-platform high-level application framework and GUI library based on the Simple DirectMedia Layer. [LGPL]
   http://www.bms-austria.com/projects/paragui/

SansGUI Modeling and Simulation Environment
   By ProtoDesign, Inc. Develop and deploy highly interactive scientific and engineering simulation programs without writing one line of graphical user interface (GUI) code.
   http://www.protodesign-inc.com/sansgui.htm

SmartWin
   A light weighted GUI C++ library for developing GUI applications in Windows API.
   http://smartwin.sourceforge.net/

TOAD GUI Library
   A Simple and Powerful C++ GUI Toolkit for the X Window System.
   http://www.mark13.org/toad/

The Lit Window Library
   An open source project aimed at making UI coding easier. The C++ library introduces rules-based UI coding, reflections and several other mechanisms to speed up UI coding.
   http://www.litwindow.com/Library/

V
   A freeware portable C++ GUI framework for Windows, X, and OS/2.
   http://www.objectcentral.com/

V C++ GUI framework library
   Portable, easy-to-use, LGPL. by Object Central, home of the book: Essence of Object-Oriented Programming.
   http://www.objectcentral.com/vgui/vgui.htm

Vermont Views Plus
   A C programming library for creating cross platform user interfaces across Unix, Linux, Posix, VMS, DOS and Windows.
   http://www.vtsoft.com/products/vviews4.html

Visual Component Framework
   C++ framework created to provide platform GUI framework, features such as Java and Java's Swing, and Borland's Visual Component Library. [Open source, BSD License]
   http://vcf.sourceforge.net

Windows++ Code Library
   A lightweight C++ application framework for Windows.
   http://www.dilascia.com/wpp.htm

Ygl
   Emulates SGI's GL routines under X11. It compiles fine under AIX 3.2, HP-UX 7.0/8.0/9.0, Linux with XFree, SunOS, ConvexOS and others.
   http://www.thp.uni-duisburg.de/Ygl/ReadMe.html

aedGUI
   A cross-plataform, easy-to-use, non-intrusive C++ GUI library that runs on top of SDL. [Open source, LGPL]
   http://aedgui.sourceforge.net/

easyGUI
   API toolkit for developing GUIs with LCD driver library graphics and graphical display controller drivers. Graphic LCD module application using advanced features like proportional writing, icons, lists and scroll boxes, line drawing.
   http://www.easygui.com/

libUFO: UI For OpenGL
   A C++ based core library for GUIs. Uses OpenGL as drawing library and SDL/Glut as windowing toolkit. [Open source, LGPL]
   http://libufo.sourceforge.net

libuta
   Based on the Simple DirectMedia Layer (SDL). Allows to put together portable graphical applications.
   http://libuta.sourceforge.net/

sjgui
   A GUI framework for use in interactive OpenGL applications. The main goal is to provide very easy and fast way to develop portable interactive interfaces, using object-oriented approach. [Open source, BSD License]
   http://sjgui.sourceforge.net/

xfsft
   Patches to provide TrueType font support for X11.
   http://www.dcs.ed.ac.uk/home/jec/programs/xfsft/