In the good ol' days of the Internet when everyone had every service running on their machine that they could imagine, people would run a FingerServer. This would let you "finger perry@storm" and it would tell you a little bit of information about me (My Realname, office, phone number, and if I was logged in etc). This could also display information about what projects you were currently working on, which would be displayed from a file called "/.plan". So it's been traditional to write a bit about what you're working on in your ".plan", although this file may no longer actually be in your home directory, called ".plan" and the machine is probably not running a finger server :)