Desktop Environments
Archy, GEM, GNOME, KDE, Alternative Linux Desktop Environment, arm0nia project, DesktopX, DeXtop, EDE - Equinox Desktop Environment, foXdesktop, Future GUIs, GUIdebook, Hooray for Bluecurve, Smashplay
Display Managers
Embedded Systems Stuff, Fresco, GGI Project Homepage, MicroWindows, Microwindows - Enabling graphical applications on , Microwindows for Personal Basis Profile, PicoGUI, Yahoo Groups: giotto-gui
Morphic
A John Maloney page, Getting Started with Morphic, Janak on Morphic UI, Morphic - The Squeak User Interface, Morphic Sample - The Scrabble Game, Programming in Morphic, Prototype-Based Application Construction Using SEL, Short Morphic tutorial, Sun Labs: Self papers, The Self-4.0 User Interface
Toolkits
Amulet, FLTK, Gtk, Motif, Qt, wxWindows, aedGUI, Bluestone Consulting (BCI), Droplets, easyGUI, FOX GUI Toolkit, General Graphics Interface (GGI), General Interface, GLO GUI Library, GNUStep, GraphApp
X11
Applications, Servers, Vendors, Window Managers, Broadway Project, DialoX, Freedesktop.org, Inter-Client Communication Conventions Manual (ICC, Keith Packard - Papers and Talks, New Rendering Model for X, Open Group Desktop Technologies (X.Org), The X Window System, UTF-8 and Unicode FAQ, What is X / X Server / XFree86
Sourcebank
GUI downloads for developers.
The Y Window System
Project writing successor of X Window System. The Y design has the following features: Network Transparency, Modularity (plug-in style: dynamically unloadable and reloadable), In-server implementation of widgets, Consistency and Themeability, Support for hardware acceleration, Better internationalisation, localisation, and accessiblity. [Open source, GPL]