Official Window Maker Website  
   NeXT Step alike window manager for the X Window system on GNU/Linux.
   http://windowmaker.org

The Official FVWM Homepage  
   The standard window manager for linux, stable but not as pretty as Window Maker or Enlightenment.
   http://fvwm.org/

Welcome to the 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.
   http://vcf.sourceforge.net

InputGUIDO  
   A GUI being developed for older DOS systems that are incapable of running Windows.
   http://www.trhonline.com/input/

Java Gui Builder  
   An engine that reads XML files describing graphical user interfaces layout.
   http://jgb.sourceforge.net/

ObjectCentral - V  
   A free, multiple platform C++ graphical user interface framework.
   http://www.objectcentral.com/

FOX GUI Toolkit  
   An open source cross-platform C++ based Toolkit for GUI development.
   http://www.fox-toolkit.org/

KronoJunior  
   Open source GUI for less powerful or old computers.
   http://kronojunior.sourceforge.net/

Prima  
   Toolkit for multi-platform GUI development. (Perl) [OS Independent]
   http://www.prima.eu.org/

GUIS  
   Open source widget server. (Python, Ruby, GTK2) [OS Independent]
   http://starynkevitch.net/Basile/guisdoc.html

CockTail - The Java RAD & WORA Tool  
   CockTail is a Java RAD & WORA Tool used to develop GUI & Swing based user interface for applications
   http://www.applese.com/products/cocktail/cocktail.html