A Briar user can either create a new forum, or get invited via a Briar contact that is already in an existing forum. There's some more info on this topic in Briar's user manual if you're interested: https://briarproject.org/manual/
Briar also has the ability to introduce contacts to each other, so while it doesn't support totally public forums, you can spread information between contacts fairly effectively.
Briar also has the ability to introduce contacts to each other, so while it doesn't support totally public forums, you can spread information between contacts fairly effectively.