"Cloudmakers" is a web-based game built around the release of Steven Spielberg's "A. I." movie, and was an amazing online puzzle which had thousands of people uniting to solve cryptic clues, crack passwords, and find out who killed Evan Chan, a minor character in the movie This "is" the future of online gaming, or at least, a breathtaking version of it.

So, multiple web domains in different countries were registered, literally hundreds of lovingly custom web pages created, and thousands of people collectively banded together online. During the course of the game, players could receive emails, faxes, phone calls, and even go to real-life meetings to advance their understanding of the amazingly intricate story. So there were literally 7000 people collectively scanning the web, solving the puzzles, even sometimes by 'unfair' means (brute-forcing passwords, using /WHOIS to find domains they weren't even meant to find yet!)

One distinctly weird part of the project is that, at the end, it was revealed that a small internal group within Microsoft (!) had created it for Spielberg + Dreamworks. This didn't even get much publicity at the time, but don't think it should dissuade people from liking the work - in fact, it's even more inspiring, in some ways, this is the "antithesis" of tedious corporate thinking.

A lot of the information you need to understand the whole "Cloudmakers" phenomenon is here.
http://pantheon.yale.edu/~dgf4/notagame/
http://www.Cloudmakers.org/
http://www.cloud makers org/guide/