How XEmacs (Lucid Emacs as was) came about, by Jamie Zawinski: '[t]his incident has become famous as one of the most significant "forks" in a free software code base'. Edited Highlights of mail-lists as events unfolded.
A graphical front-end to xmodmap. It opens a window that looks like a keyboard; moving the mouse over a key shows what KeySyms and Modifier bits that key generates. Clicking on a key simulates KeyPress/KeyRelease events on the window of choice.