You can form a discussion group on the Fediverse using Guppe, a new service at:
You can follow a group's posts by following its account, and take part in the discussion by mentioning that account in a message.
You can also start a new group by mentioning it in a message.
You can see a list of existing groups on the site at https://gup.pe
gup.pe looks really neat for adding discussion groups (of a sort) to the Fediverse. It really needs to be open source, as otherwise it's just another single point of failure.
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