An old, old Internet protocol that was used to get information on a user, and could be used by users to post updates from their .plan files. Essentially plaintext social media for people with Internet connections in the 80s and (early-ish) 90s.
Reimplementing it (well, the CLI program, `finger`) also happens to be the final exercise of Haskell Programming from First Principles, after 1200 pages of glorious buildup from the lambda calculus forward, in case that sells anyone on trying it ;)
I had that "oh crap, I'm old" moment when my initial reaction was "what? You've never heard of finger?!" and then I remembered I last used it in the late 90s.
I'm glad your reaction was to assist the young folks. :)
