Back in the day (around 1996 - 1998), I worked with a number of people from the DC Heroes RPG e-mailing list to put together an enhancement supplement for the game system, which was no longer being published. The document produced was referred to as The Unofficial 4th Edition, a direct supplement to DC Heroes RPG: 3rd Edition from Mayfair Games. It was freely available online for some time.
The document was polished and subsequently published by Pulsar Games as The Sidekick Sourcebook, to expand (and patch) their base Blood of Heroes RPG (essentially a reprint of the aforementioned DCH 3rd Edition rules). Contributors were given a large discount to purchase the product, and the interest at the time effectively assured it would be produced (sort of pseudo-crowd-funding). The rules were later imported directly into their comprehensive rulebook product, Blood of Heroes: Special Edition, making Sidekick Sourcebook somewhat obsolete.
As the contributions to the document were culled from varied sources and rules were determined through evaluation of in-depth debate and discussion, I felt that Sidekick worked as an example of an online, crowd-sourced project (working directly multiple people from disparate sources agreeing and disagreeing on rules, to create a final product).
I realize that while it was produced somewhat early in the age of the internet, Sidekick probably was not the first crowd-sourced pen-and-paper RPG product. Historically, is there a first (digital and/or analog), and if so, what is it?
I'd like to know how far back this sort of thing goes.
Note: some answers I've received are compilations of mostly prior works (previously published articles, for example). While that probably qualifies in the spirit of crowd-sourcing, what I would prefer as an answer would be something created by contributors actively polled for content, deliberately worked together for the sake of achieving the goal of a centralized document.