Jamie Zawinski has an interesting old post on Emacs history. It’s a timeline of Emacs versions from Stallman’s, Moon’s, and Steele’s original merger of TECMAC and TMACS in 1976 to Gnu Emacs 22.1 and XEmacs 21.4.21 in 2007.
His original timeline was written in 1999 and then updated in 2007. I wish he would update it again, although the history since Emacs 22 probably isn’t that interesting. In any event, if you enjoy exploring the history of our field and Emacs in particular, you should give this post a look.