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

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

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/

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/

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

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

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/

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/

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

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

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/

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

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

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

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/

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/

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

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/

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

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

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

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

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

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/

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

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/

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/

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/

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/

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/