"Canvas" is the only other one that's been posted here*. It was a pixel art thing with a shared grid that ran for a day (maybe a little more or less) and users had to wait between their edits. Less risk of a single person blanking the whole thing or filling it up with nazi trash.

Looks like this community is here for if Canvas comes back (think it was an annual Reddit thing before it was here so they might follow suit). If not, maybe there will be something else like a game or scavenger hunt or whatever else that users from federated instances could collaborate on. Remains to be seen.

* I'm wrong, there were also some music-based events. Those were also only open to users of federated instances.