I enjoyed this 1979 article on #Emacs by Stallman. I'd read some old papers on Emacs already but what struck me of this one was to see how much Emacs was there already in 1979!
https://archive.org/details/MITAIMemo519
The extensibility and the fact that the editor documents itself, one'd expect them from the start because they're so foundational. But #Dired was also there already and so was Rmail, a mail client apparently.
I'd be curious to try a very very old Emacs version and see how it feels to someone 45 years from the future. I'm not even sure if such an old version could be built or run these days though?
@fabionatali earlier this year I contacted Bernard Greenberg, who was the central force behind the development of Multics Emacs, and I learned a lot of striking things
https://functional.cafe/@PaniczGodek/112220185865167284