Mastodon is an open-source social network made up of independent servers. You can publish text, photos, audio, video and polls, follow accounts on other servers and read their posts in a chronological home feed.
You can join an existing server or run your own. Each operator sets its own rules and moderation policy; registration and hosting arrangements vary. ActivityPub connects Mastodon with compatible services elsewhere in the fediverse.
Source: Product overview
