Invite-only and self-hosted are different things.
Discord is invite-only but not self-hosted. Maybe that would work for you?
Discord is invite-only but not self-hosted. Maybe that would work for you?
scuttlebutt https://scuttlebutt.nz/
twtxt https://indieweb.org/twtxt
iris.to (hypercore protocol)
meshtastic https://meshtastic.org/