Knights of the Lambda Calculus - A group of expert Lisp hackers that formed out of MIT. Membership is known to have been granted to those who passed MIT's Spring 2004 Structure and Interpretation of Computer Programs course, but reality beyond this point becomes unclear. The Jargon File attests to their existence.
The Birthday Party - A political party attempting to elect a shadowy and mysterious nobody. This "nobody" is said to care, listen, understand, be perfect, should have "too much power", and even make pies better than mom.
Black Wings Society - According to the foreward in modern editions of their "Book of Rok", the Black Wings have their roots in centuries-old occult groups. Presumably disbanded in 1996, their 2017 revival contains notes on technology and history from up to at least the year 2186.