I'm sure there are more than a dozen and you are right. I'm still trying to get the hang of the whole fediverse thing, but so far most of the more niche communities I have tried to interact with are on different servers not federating with each other? Or maybe I'm doing something wrong? Not sure about that one. Also not sure if cross-posting works. I mean I know it works, but do those posts federate correctly? Can other fediverse apps see them correctly?