Lemmy has a feature for taglines where you'll see a random one on every refresh. We used to have a selection of a few communities in there, but at this time we don't have anyone available who has spare time to maintain this. We're open to suggestions or even someone joining e.g. our matrix and we'll be happy to set up a group chat for collecting communities and adding/rotating them in our list.

This is instance specific, so each instance has to maintain this on their end.

At the moment we have only !newcommunities@lemmy.world and !communitypromo@lemmy.ca in the list.

I was under the understanding that an admin would put out a blanket message and you could vote for your favorite ones. But it can't be the same community every month. I found some pretty niche communities that way and plus it give the little communities a place to shine for a couple days.