> It's quite difficult to find software older than Emacs in widespread use.
Agredd! Aside from the basic Unix commands (ls, cat, etc), the only substantial program that I use today that I also used in 1991, is emacs.
Well, and perl. I don't write much perl these days, but I have tons of perl scripts accumulated over the decades that I use daily so that counts as using it.
Third oldest for me would be mutt, which is still my primary email client. But I only switched from elm to mutt in.. not sure maybe 1996?