The fediverse (a portmanteau of ‘federation’ and ‘universe’) is an ensemble of federated (i.e. interconnected) servers that are used for web publishing (i.e. social networking, microblogging, blogging, or websites) and file hosting, but which, while independently hosted, can communicate with each other.
Their are federated alternatives to many mainstream websites: PeerTube (YouTube); Funkwhale (SoundCloud); Mastodon, Hubzilla, and pump.io (Twitter); Frendica (Facebook); Drupal (WordPress); Pixelfed (Instagram); and Lemmy (Reddit).
On different servers (technically ‘instances’), users can create so-called ‘identities.’ These identities are able to communicate over the boundaries of the instances because the software running on the servers supports one or more communication protocols that follow an open standard. As an identity on the fediverse, users are able to post text and other media, or to follow posts by other identities. In some cases, users can show or share data (video, audio, text, and other files) publicly or to a selected group of identities and allow other identities to edit other users’ data (such as a calendar or an address book).
In 2008, the social network identi.ca was founded by Evan Prodromou. He published the software GNU social under a free license (GNU Affero General Public License, AGPL). It defined the OStatus protocol, an open standard for federated microblogging, allowing users on one website to send and receive status updates with users on another website. Besides the server, identi.ca, there were only few other instances, run by persons for their own use. In 2011, identi.ca switched to another software called pump.io. and several new GNU social instances were created. Other projects, such as Friendica, Hubzilla, Mastodon, and Pleroma integrated the OStatus protocol, thus extending the fediverse (though Mastodon and Pleroma later dropped OStatus in favor of ActivityPub).
In 2018, the W3C, the main international standards organization for the web, presented the ActivityPub protocol, aiming to improve the interoperability between the platforms. It quickly became the dominant protocol used in the fediverse, however OStatus is still a commonly used protocol along with Diaspora Network and Zot & Zot. The software on fediverse platforms are FOSS (Free and Open-Source Software). Some of them vaguely resemble Twitter in style (for example, Mastodon, Misskey, GNU social, and Pleroma, which are similar in their microblogging function), while others include more communication and transaction options that are instead comparable to Facebook (such as is the case with Friendica and Hubzilla).
A number of developers publish live statistics about the fediverse on monitoring sites like the-federation.info. The statistics on these sites are an indication of usage levels, not a complete record, as they can only aggregate data from instances that use the NodeInfo protocol to publish usage statistics. There is no guarantee that all instances are known to these sites, and some instances may disable NodeInfo, or use software that hasn’t implemented it. Some of these sites include data from any federated software that publishes it using NodeInfo, not just fediverse software.
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