I'm curious as to whether anyone has tried to build the setting world as a group-wide collaborative effort, and what the results were?

I think there could be some real benefits to this: reduced workload on the GM, the Players get to influence the world toward the kind of world that they want to play in, increased Player "buy in" for the world, etc.

I'm aware there are actual world building games that could leveraged for this, like Microscope - although I've never tried it.

I think that it would work better with the GM as "creative control" or "editor" - but maintaining a fairly loose leash.

I also realize that this takes a particular type of player; some players really don't care about this level of detail.

I'm curious as to what people think of this approach, if anyone has tried it ( successfully ), and what are the issues that you may have run across?

I think that's a great idea. I mean, granted, it would only really work if you have a group of very committed and relatively mature players. And it would greatly extend the period of time before the beginning of a campaign. I mean, instead of a Session Zero, you'd have to have a dozen or so Sessions Zeroes to build the entire world and to discuss/debate all the different elements - geography, politics, religion, etc - and how they fit together. 

Maybe each player, during character creation, could also create the home city or home area of their character, with notes about general placement (coast, desert, farmland, etc) and the DM could just plug that city or village into an appropriate area on their map. 

And maybe each player is a member of a faction or a guild or is a graduate of some Academy or Temple. And so they get to create that organization as well. And the DM just plugs it in where it fits. 

Of course, the DM will still be responsible for the vast majority of the homebrew worldbuilding effort. Partly because any DM who wants to create an entire homebrew world must already have some pretty solid ideas on hand, and partly because coordinating a bunch of players in such a massive project will be a bit like herding cats. 

Personally I'd love to be in a group that tries something like that. I think it's a great way to help the players feel invested in the campaign setting. 

I've done something similar, although on a much smaller scale regarding my players.  Basically, there's a piece of advice I came across a while back to let your players make something in the world that ties in to a character's backstory, be it a town, an organization, etc that lets them have a personal touch to your world.  Thus far my players have used this rather sparingly, but even then it's proven to be a catalyst for some of the best ideas I've had for the campaign I'm running.

I like the idea of putting the Players in charge of making the part of the world around their Character. You're more likely to get them to do it, since it benefits them ( or at least benefits the Player who values role-playing; your tactical war gamer style Players probably still won't care much ).

I agree that collaborative setting building would stretch out your Session Zero(s), but you might not need a dozen or so, if you take a particular approach to world building. My approach is what I liken to cardboard movie sets. Everything the Characters look at or interact with seems fully developed, but the actual details might not be decided upon until they're needed. The local town is fully designed. The next town over is only designed so-as to provide enough information for the local NPCs to talk about it realistically. The next country over, the same way, with lesser detail - so that the further away something is from the Party ( or anywhere the Party has been ), the less canonical information has been created. Of course, you need a double handful of detailed legends and rumors about far off places & people so-as to provide alluring potential adventure hooks, as well.

The idea here is to reduce the creative workload on the GM, allow them to focus their creative energies efficiently, and help prevent them from falling down the hole of World Builders Disease.

The trick with that approach is making sure that the spur of the moment design choices made is response to Player actions are consistent, so a lot of quick thinking, note taking, and post-session write up and "tinkering" with the newly revealed facets of the world to make them fit. There's also the danger of leaving out details that you think would be irrelevant to day-to-day life, but when you create them discover they have wide-reaching effects. For example, you might only sketch out a few major deities in your world, but it may turn out that your world's religions end up having a large impact on the day-to-day customs of the people, so those are effects you probably should have been taking into account even for the first Party/Shopkeeper interaction. 

Personally, I'm struggling with trying to decide what is just enough detail to make the world look complete, without any retroactive consistency issues cropping up when something is decided upon.

However, if you keep the up-front designed details to a minimum, then the collaborative workload isn't that bad, and if the Players want to contribute more detail than is needed for something - that's OK.

I have had an idea with someone that we could play a finish the story kind of DND. We wrote a sentence and handed it to the other, and another person DMed it. He ended up using half of it after having some ideas, because we were doing it because he didn't want to write but wanted to DM a campaign like the ones we write.

Was fun, I also had an idea of something like that on dnd beyond as a thread.