Xplain – Explaining X11 for the rest of us
Personally, my favorite explanation of X11 is found on page 139 of the Unix Hater's Handbook http://web.mit.edu/~simsong/www/ugh.pdf"A truly portable X application is required to act like the persistent customer in Monty Python’s “Cheese Shop” sketch, or a grail seeker in “Monty Python and the Holy Grail.” Even the simplest applications must answer many difficult questions"Read the original for the hilariously accurate dialog that follows…