Ie similar to how Lemmy allows users to create instances that are federated with each other, only this Discord alternative’s instances wouldn’t federate with each other.
Instead, each instance would be a complete silo, although instance owners would be given the option to potentially federate their instance outwards (ie to other federated platforms), if they wish.
Perhaps it could potentially be forked from the already existing Lemmy?
https://www.windowscentral.com/software-apps/discord-alternative-search-10000-percent-stoat
https://www.zdnet.com/article/discord-age-verification-requirement/


What are the critical features of Discord?
Other less-critical but still potentially important features:
I don’t know of any that cover all of those, and ymmv on how critical some of these are.
Movim (an XMPP client) covers most of that. I think it’s currently working on having a collection of rooms be in one channel, but it already has group chats, group video calls, screen sharing, and permissions in groups.
It doesn’t have forums in it, but it does allow users to have blogs.