Fediverse

The fediverse (commonly abbreviated to fedi)  is a collection of social networking services that can communicate with each other (formally known as federation) using a common protocol. Users of different websites can send and receive status updates, multimedia files and other data across the network. The term fediverse is a portmanteau of "federation" and "universe". The majority of fediverse platforms that are available are free and open-source software, and are based on the ActivityPub protocol. However, alternative protocols such as AT Protocol and Nostr have formed their own networks separate from ActivityPub.

Design
While a traditional social networking service will host all its content on servers managed by the owner of the website, the decentralized servers that make up the fediverse allow any individual or organization to host their own servers (referred to as an "instance").

Every instance is independent, and can set its own rules and expectations. Even so, much like how users of one email service such as Gmail can still send emails to users of another service such as Outlook, users may still view content and interact with users on any other instance in the fediverse. A user on one Mastodon instance, for example, may still view and interact with posts made by a user on a different Mastodon instance.

Instances hosted by different social networking services may communicate with one another as well. A user on the microblogging platform Misskey, for example, may view and interact with posts made by users on Mastodon. Some fediverse networks even allow users to interact with different social networking formats from the same platform. For example, a user on a social news instance running Lemmy can interact with another post from a kbin instance, a similar service as well as microblog statuses from Mastodon.

Historical protocols
The concept and the functionality of the fediverse has existed before the ActivityPub protocol and the term itself. One of the first projects that included support for a decentralized social networking service was Laconica, a microblogging platform which implemented the OpenMicroBlogging protocol for communicating between different installations of the software. The software was later renamed to StatusNet in 2009, before being merged into the GNU social project in 2013 along with Free Social, with the two latter servers being a fork of StatusNet.

Over time, the limitations of the OpenMicroBlogging protocol began to show, as it was designed as a one-way text messaging system. To replace the aging protocol, OStatus was devised as an open standard for microblogging, combining various other technologies like Salmon, Atom, PubSubHubbub and ActivityStreams into a single protocol used for communicating between instances. StatusNet first implemented the protocol in March 3, 2010 with version 0.9.0, and quickly became the most popular federated protocol in usage.

Around the same time as OStatus was gaining popularity, the Diaspora (stylized as diaspora*) social network was formed, using its own federated protocol. To illustrate the differences between the two protocols, the terms of the fediverse and the federation began to enter common usage, mainly after 2017. The term "the fediverse" was used to describe the network formed by software using the OStatus protocol, such as GNU Social, Mastodon, and Friendica, in contrast to the competing diaspora* protocol under "the federation".

ActivityPub
In December 2012, the flagship GNU social instance at the time, identi.ca, began to transition away from OStatus to a new protocol named Pump.io. The new protocol was designed to be useful for more than just status updates, and replaced Salmon, Atom and PubSubHubbub with JSON-LD and a REST API for its messaging and inbox systems, as well as making more use of ActivityStreams. While not as active and developed as its OStatus predecessor, it would end up becoming influential in the development of the ActivityPub standard.In January 2018, the W3C presented the ActivityPub protocol as a recommended standard. The standard aimed to improve the interoperability between different software packages running on a wide network of servers and to succeed both the OStatus protocol and Pump.io. By 2019, almost all software that was previously using OStatus had removed the protocol in favor of ActivityPub (Friendica being a notable exception, including support for OStatus and diaspora* along with ActivityPub), and the term fediverse has since come to mainly refer to the ActivityPub protocol and its supporting server software.

Adoption
For most of its history, adoption of the fediverse from users had been minimal due to its poor user experience and over-reliance on technical details and complex terminology, as well as from existing platforms due to a lack of general interest among their userbase as well as development costs outweighing any potential benefits.

Following the acquisition of Twitter by Elon Musk in November 2022, certain major social networks, including Threads, Tumblr and Flipboard have expressed interest in supporting the ActivityPub protocol, as a large number of users began to migrate to Mastodon, a server that supported the fediverse and was also the most popular alternative to Twitter at the time. Flickr had also expressed support in supporting ActivityPub, however no information was released by the company after the initial tweets by the CEO and is suspected to be on hold or cancelled.

Microblogging
Automattic CEO Matt Mullenweg tweeted on November 22, 2022 that Tumblr was adding support for ActivityPub interoperability, in response to a user's complaints about Mastodon's complexity. However, no further information was revealed for over a year, and was expected to be cancelled after a leaked reorganization that moved most of Tumblr's staff to other Automattic projects. However, in an AMA following the leak, he revealed that the interoperability feature was not cancelled and that there was a small team working on studying the potential of implementing the protocol.

The release of Threads by Meta in July 2023 had included in its press release that it planned to support interoperability with the ActivityPub protocol in the future. In December 2023, select Meta employees began to federate with ActivityPub. A roadmap was revealed in January 2024 that detailed the integration of ActivityPub in Threads.

In March 2024, Threads implemented a beta version of fediverse support, allowing Threads users to view the number of fediverse users that liked their post, and allowing fediverse users to view posts from Threads on their own instances. On April 2, the official Threads account for President Joe Biden enabled federation on its profile, making Biden the first President of the United States to have a presence on the fediverse.

News aggregators
In December 2023, Flipboard announced that it has begun to federate selected profiles and magazines with the fediverse. It had previously ran its own Mastodon instance, flipboard.social, as a test of the fediverse.

Content management systems
Hubzilla is a CMS for federated Hubs with also ActivityPub connectivity. Hubzilla provides blogs, articles, calendars/events, a cloud storage and much more. It works with WebDav, CalDAV, CardDAV and provides an access and permission system which works across Hubs and fediverse instances. WordPress has an officially supported plugin that integrates WordPress blogs into the fediverse, allowing for comments to be exchanged between the comment section of a blog post and a fediverse instance's reply function. The plugin was acquired by Automattic in March 2023, and became available for all WordPress.com users in October of that same year. Ghost, a blogging platform and content management system similar to Substack announced in April 2024 that they would be implementing fediverse support via ActivityPub. Previously, the feature had been highly requested on the Ghost forums, becoming the second most voted feature request in its forum category.

Software

 * ActivityPub, a W3C standard, is the most widely used protocol in the fediverse. Some popular fediverse software includes:
 * Content management system
 * Drupal (via third-party plugin )
 * Hubzilla
 * WordPress (via official plugin )
 * Image sharing/Video sharing
 * Pixelfed, an Instagram alternative
 * PeerTube, a video streaming service similar to YouTube
 * Macroblogging
 * Diaspora
 * Friendica, an alternative to Facebook written in PHP
 * Microblogging
 * Mastodon, a microblogging social network written in Ruby
 * Misskey, a popular Japanese social network written in TypeScript
 * Pleroma, a lightweight microblogging server written in Elixir
 * Social news
 * kbin, written in PHP
 * Lemmy, a Reddit alternative written in Rust

Statistics and software overview

 * Fediverse Observer
 * Fediverse Party
 * FediDB
 * The Federation
 * The Fediverse Explained: Social Media’s Next Form

ActivityPub specification

 * ActivityPub
 * ActivityStreams Core
 * ActivityStreams Vocabulary