Discord

Discord is a chatroom app, originally developed for voice. In fannish contexts, it is primarily used for its Slack-like text features.

Discord servers are free to run at any scale. (It makes money off of game subscriptions and merchandise sales.)

Server structure

A typical fannish outpost on Discord will tend to have these text channels:

A welcome channel, placed at the top of the channel list where new arrivals land, with a single message welcoming them, presenting rules specific to the server, and/or directing them to channels they might find useful.
A channel for news or announcements only.
A help channel.
A channel for general chatter about the event, topic, or community the server is for.
A channel for off-topic chatter.
Channels for notable subsets of the community, such as fans with a particular sub-interest, or speakers of a particular language.