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Unix GUI/X Windows 
Introduction to X Windows KDE 2.0 Development [Mirror]
XEmacs Tutorial XView Programming and Reference
Grokking the GIMP The GIMP User Manual [Homepage]
Writing GNOME Applications GTK+ / Gnome Application Development
GTK+ Tutorial GTK+ Reference Manual
Cygwin User's Guide Wine How-To
X Window System Architecture Overview (D. Manrique) An Introduction to Tkinter
X Window and Motif Programming Guide (D. Marshall) Xlib Programming Manual [Mirror] [Mirror]
Xlib programming: a short tutorial XLib Manual [Mirror] [Mirror] [Function Index]
Motif Programming Basic Graphics Programming with Xlib Library
Xlib Reference Mannual [Mirror] AIXwindows Programming [Mirror] [Mirror]
Motif Programming Manual (6A) / Motif Reference Manual (6B), 2nd Ed [Mirror] [New Version]
XView Programming Manual (7A) 3rd Edition and XView Reference Manual (7B)