From Mastodon, MHoye posting at
https://mastodon.social/@mhoye/112615649865163136:

I haven't seen anybody mentioning it or even noticing it, like it's just
the water we swim in now, but this month marks the fiftieth anniversary of
the release of what would become a seminal, and is arguably the single most
important, piece of social software ever created.

Written by Douglas McIlroy and James Hunt and released with the 5th Edition
of Unix this month in 1974: diff.

https://minnie.tuhs.org/cgi-bin/utree.
<https://minnie.tuhs.org/cgi-bin/utree.pl?file=V5/usr/source/s1/diff1.c>..