It is a forum application where each community is invite only. Think a cross between reddit/discord. The invite only architecture reduces trolls, spam, AI slop and promotes more substantive discussions.

Right now invitations are limited to 1 per day for each user in a community. You don't need an invite to join at the global level - but to join any community you must have received an invitation link. Still a major work in progress, right now working on expanding the flexibility of community creation and invitation logic. (allowing bulk invites, adding flexible invitation cool downs, etc).