How do large community events, games, quiz projects, etc. work? Are they started by the site management, by users, both? Are they official things or informal (for example, I haven’t been able to find like an official info page anywhere for the MCCQ project, just a bunch of quizzes involved in it)? Do they have pages somewhere? Do you have to be a certain level to participate? I’m interested in how these work.
More 'events' to be involved in include joining groups.
The Interesting Facts (ask IFGroup or Neodymium if you want to join), Quiz Advertisement Group (contact Pontiac) and JetPunk Magazine Group (run by LuckyCat) are some places to be involved.
The MCCQ project started with QM making a few, before users all made their own, so it started being something big.
As for the game things, you just sign up like what zarodinu said
Groups are another great way to hold an event.