The history of the .plan file goes back to way before ID or Carmack. It's been part of unix for a long time. Back when things were simpler, you could finger a user and read their .plan to see what they were up to.
For a brief bit I had a simple python script dump tweets into a .plan file mostly just to amuse myself by connecting new social media to old.
Hmm, I wonder if I ask my Mastodon host nicely if they'd open up finger protocol support, lol. (ETA: Reminds one of the old adage about blind men touching the elephant.)
