RFC-742... something so antiquated, yet so refreshingly useful.
Roughly speaking, it is a text-based internet identifier/status service. A server responds to a finger request with some snippet of info about the server or person. This could be contact info. This could be current status info in a '.plan' file. Sky's the limit, so long as it is plain text.
When you really get down to it, it was a primative (and in some ways *better*) microblogging service.
You want to know about your buddy `cooldude@coolplace.net`, you finger it and get back the info. Or if you wanted to see what his host server was about, you finger `@coolplace.net` to get the low-down.
Fucking brilliant.
With the modern internet funneling down to fewer and fewer propretary services, looking back at the early web is inspiring. You don't have a dozen accounts for social media/web/etc. you have a host that gives you access to various protocols: pop/imap mail, usenet newsgroups, ftp and http (or gopher) hosting, and if they are really rad, finger. In this way, you have a homestead on the internet. You have a single identity, or if you need multiple identities, you perhaps have one at your work and one with your dialup host and one with a community unix server, so you can keep your life seperate. However, each segment could potentially have a "complete" complement of internet presence, entirely independent of each other.
It may seem that I am ranting about something that is meaningless or easily done today [mail with Gmail and microblogging with Twitter and Tumblr and community stuff on Discord or Reddit], but in the old way, you own your space, you are not under constant survellience, and everything is low-bandwidth and shareable. The web is made up of people and each have content to be discovered.
Returning to finger, however, what is returned is not just user/server info or .plan or .project files... Servers can return any sort of live information. Hell, Carnegie Mellon University used to have a Coke machine that would tell you when it was loaded and if it was cold via finger [1]. Clearly, Internet of Things predates the modern web.
More modern madness is `typed-hole.org`. Fingering `@typed-hole.org` will bring up guide showing how to get user info, user feeds and phlog entries, cpu temp, ezines, weather, and even a choose-your-own adventure story via finger.
If you are in the tildeverse/public unix servers, you probably have access to finger. If you have your own host, well, just install finger and fingerd, populatesome files with content, and chmod them so they are accessible. A good tutorial is here [2].
I think with a rise in people returning to text-based internet, alternate nets like gopher and gemini, finger should be part of the arsenal as well.
[1] CMU SCS Coke Machine [HTTP]