A lot are on discord, but the mods are looking at an official Lemmy alternative. At the moment lemmy.ml is having significant issues so I'm not sure how that's impacting federation, but hopefully they improve their servers soon..

Personally I don't think Lemmy is really a great alternative in its current state especially with servers being able to defederate other servers, meaning that users registered on Beehaw for example can't now view communities hosted on lemmy.world which seems to entirely defeat the purpose to me..