Where Vim Came From (via) is an interesting and thorough overview of the history of vim, vi, ed, and other predecessors (with copious footnotes). It's nice to see all of the pieces laid out this way, and I learned of some historical links that I hadn't already known.

(I do wonder what vi would have been like if ed had kept QED's multiple buffer support.)

Update, the next day: See also Dennis Ritchie's An incomplete history of the QED Text Editor (via).