An open source social network is social software whose code is publicly licensed, so anyone can run, inspect and modify it. Most, such as Mastodon, Friendica and Diaspora, connect independent servers instead of keeping everyone on one company’s platform.
This guide explains how these networks work, compares the main projects, and covers the licensing, privacy and hosting trade-offs, starting with the basics of what the term covers and why it matters.
What is an open source social network?
A social network lets people create profiles, follow one another, post updates and message each other. What makes one “open source” is the licence on the software itself. The code that handles posts, follows, notifications and moderation is published, which means outsiders can audit it, fix it and fork it. A closed platform offers none of those options: users rely on the operator’s word about how the system behaves.
Open source does not automatically mean decentralised, although the two ideas overlap heavily in practice. A single organisation could publish the code for a social site and still run the only copy. The projects covered here go further: they are designed so that many independent operators can run their own servers, and those servers exchange content. Mastodon’s own documentation describes the idea plainly, saying that federation is a form of decentralization, and it lists email, XMPP, phone networks and physical mail as federated systems, while placing Twitter, Facebook and Instagram in the centralised category.
The email comparison is the most useful mental model. The same documentation notes that, just like you can send an email from your Gmail account to someone from Outlook, Fastmail, Protonmail, or any other email provider, a person on one Mastodon website can mention or message someone on another. Nobody needs an account with every provider; they need an account with one, and an address that others can reach.
Readers who want the architecture explained in more depth can read the companion guide to the decentralized social network model, which covers federation, distribution and the trade-offs between them.
How federation and ActivityPub work
Most open source social software now speaks a shared language called ActivityPub. According to the encyclopedia entry on the protocol, it provides a client-to-server (C2S) API for creating and modifying content, as well as a federated server-to-server (S2S) protocol for delivering notifications and content to other servers. The first half lets an app talk to its own server; the second lets servers talk to each other.
The standard has a clear date of origin. It was first published by the World Wide Web Consortium (W3C) as a W3C Recommendation in January 2018, produced by the Social Web Working Group. Its data format is also specified: ActivityPub uses the ActivityStreams 2.0 format for building its content, which itself uses JSON-LD. Every user is an “actor”, and every actor type contains an inbox and outbox stream. A post is published to the author’s outbox and then delivered to the inboxes of recipients on whichever servers they use.
Where the term fediverse comes from
The collective name for these interlinked servers is the fediverse. The reference entry explains that the term Fediverse is a portmanteau of federation and universe, and that the majority of Fediverse platforms are based on free and open-source software, and create connections between servers using the ActivityPub protocol.
The path to ActivityPub was not direct. The earlier OStatus protocol linked GNU social, Mastodon and Friendica, while Diaspora used its own separate protocol. After the W3C step, adoption was quick: by 2019, almost all software that was using OStatus had added support for ActivityPub. Friendica kept older protocols alongside the new one, which is one reason it still bridges so many networks.
Why open standards change the economics
A shared protocol lowers the cost of leaving. On a closed platform, a user’s audience is trapped inside the product, so quitting means starting over. With a federated network, the audience can follow an account to another server, and developers can build apps, bots and tools without asking permission. That openness also explains why publishers, blogging tools and video services have experimented with adding the protocol, since a single integration reaches many independent communities at once.
What federation means for moderation
Federation shifts responsibility to server administrators. A moderator on one instance is responsible for local users and also has to decide how to treat content arriving from remote instances. Mastodon’s founder has argued that small, closely related communities handle unwanted behaviour better than a large company’s small safety team, and that view shaped the design: each server sets its own rules and can block others. The consequence is uneven experience. A well-run instance can be pleasant, while a neglected one can leave users exposed to abuse or outages.
The main platforms compared
The fediverse is not one product. The reference list of popular software groups it by purpose: Microblogging Mastodon Misskey Pleroma Image sharing / video sharing Pixelfed PeerTube Loops Social networking Friendica Social news Lemmy Events Mobilizon. Each project targets a different habit, yet an account on one can often follow accounts on another.
Mastodon
Mastodon is the best-known example. The encyclopedia entry says it was first released in 2016 by Eugen Rochko and has positioned itself as an alternative to mainstream social media. On a standard server, posts can reach up to 500 text-based characters, greater than Twitter’s 280-character limit, though some instances allow more. The software is written in Ruby on Rails and Node.js.
Growth came in bursts tied to events at larger platforms. The global use had risen from 766,500 users as of 1 August 2017, to 1 million users on 1 December 2017. A far larger wave followed in late 2022, when weekly new sign-ups were reported at 700,000, moving Mastodon over the 7 million user mark. Release history shows steady development: Mastodon 4.0 was released in November 2022, adding translation, post editing and hashtag following, and Mastodon 4.5 was released in November 2025. Mastodon is also interoperable with other ActivityPub-based platforms, such as Threads. Readers weighing it against microblogging incumbents can see the dedicated open source twitter alternative guide.
Other projects at a glance
| Project | Main use | Notable detail |
|---|---|---|
| Mastodon | Microblogging | Ruby on Rails and Node.js; ActivityPub |
| Friendica | General social networking | Connects to Diaspora, ActivityPub and others |
| Diaspora | Privacy-focused social networking | Own protocol; AGPL licence |
| Pixelfed | Image sharing | Federates with Mastodon-style apps |
| PeerTube | Video hosting | Used by a Polish municipality in 2024 |
| Lemmy | Link aggregation and discussion | Surged during the 2023 Reddit API dispute |
Two of those entries have concrete public-sector and growth examples. The reference entry records that in 2024, the local government of the Stary Sącz municipality in Poland launched their own PeerTube instance. It also notes that during the 2023 Reddit API controversy, the decentralized link aggregator Lemmy experienced a significant surge in growth as users sought alternatives to Reddit.
Diaspora and Friendica: the older generation
Before Mastodon, two projects defined the idea of an open alternative to Facebook. Both remain maintained, and both take a different approach from the microblogging model.
Diaspora
Diaspora began as a student project. The encyclopedia entry states that the founders started the project after being motivated by a February 2010 speech of the Columbia University law professor Eben Moglen, and that the work was done by four students at New York University’s Courant Institute. The public responded: the group received crowdfunding in excess of $200,000 via Kickstarter. A consumer alpha version was released on 23 November 2010.
The architecture is built around pods. Each pod (node), however, is owned and operated by a different provider, so no single party controls the whole. The code is licensed under the terms of GNU-AGPL-3.0. Its infobox lists a stable release of 0.9.1.0 / 7 April 2026 and a user count of 859,000+, figures that reflect the page as retrieved in November 2026.
One quirk matters for newcomers: Diaspora is the only actively developed software project classified under the original definition of Fediverse that does not support ActivityPub. Users can still interact with other networks through bridges such as Friendica, but it is not a native ActivityPub participant. A fuller profile appears in the guide to diaspora.
Friendica
Friendica is the bridge-builder. The reference entry says users can connect with others via their own Friendica server, but may also fully integrate contacts from other platforms including Diaspora, Pump.io, GNU social, email, Discourse and, more recently, ActivityPub. It also describes the project as one part of the Fediverse, an interconnected and decentralized network of independently operated servers.
Reviewers have long compared it to the mainstream incumbent. A PCMag review described it as mostly comparable to Facebook, and one magazine walk-through noted that Friendica does not require any specific hardware, so you can use an old computer system as a server. The project’s own site says Friendica runs on PHP with MySQL as a database, and adds that if you can run WordPress, you can run Friendica. The platform suits people who want long-form posts, groups, events and multiple profiles rather than a short-post timeline. See the friendica guide for setup notes, and the open source facebook alternative comparison for how it stacks up against other options.
Protocols beyond ActivityPub: Bluesky, Matrix and relay networks
ActivityPub is not the only open design. Several projects use different foundations, and each makes a different trade-off between openness, scale and simplicity.
Bluesky and the AT Protocol
Bluesky is the highest-profile alternative. The encyclopedia entry says it was developed as a reference implementation of the AT Protocol, an open communication protocol for distributed social networks, and that it is owned by Bluesky Social PBC, a benefit corporation based in the United States. That ownership structure is a key difference from Mastodon’s server-by-server model: the protocol is open, yet the flagship service is run by one company. The protocol’s own site describes the AT Protocol as a data network and frames it around the goal of Building the Social Internet.
Its timeline is well documented. Bluesky was launched as an invitation-only iOS beta on 17 February 2023, and it opened registrations to the general public on February 6, 2024. Registered users then climbed fast, rising from 3.14 million to 5.1 million in one month.
Matrix, Nostr and Farcaster
Matrix is a federated messaging protocol rather than a timeline network, but it shows how open standards reach institutions. The reference entry says Amdocs then funded most of the development work from 2014 to October 2017. Encryption is available as an option: the Olm library provides for optional end-to-end encryption on a room-by-room basis. Government use followed, including the French messenger Tchap, which was open-sourced and released on iOS and Android in April 2019, and a German defence pilot that began in December 2019 under the name BwMessenger.
Relay-based designs are a further branch. The reference entry notes that smaller competitors such as Nostr and Farcaster have become popular within the cryptocurrency community, and that they publish content to relays rather than ActivityPub’s server-centric model. Anyone choosing a network should check which protocol it uses, because that determines which other services it can reach.
Licensing, privacy and hosting trade-offs
Why the AGPL matters
Both Mastodon and Diaspora use the GNU Affero General Public License, a licence written for software that runs on servers. The Free Software Foundation describes it as a free, copyleft license for software and other kinds of works, specifically designed to ensure cooperation with the community in the case of network server software. The practical rule is that it requires the operator of a network server to provide the source code of the modified version running there to the users of that server.
Compliance is not guaranteed. The Mastodon entry records that some operators do not release their source code modifications, violating the AGPLv3 license in use by Mastodon. A licence gives users a right, but only people who check and enforce it benefit from it.
Privacy: better defaults, not a guarantee
Open source networks typically collect less personal data than advertising-funded ones, which lowers the value of any breach. They are not immune to flaws, though. Configuration errors and security bugs in server implementations have led to user data being scraped or modified. Direct messages on most federated servers are readable by the administrators involved, so sensitive conversations still call for end-to-end encrypted tools. A broader treatment lives in the guide to privacy-respecting social networking.
Choosing a server wisely
Because the server is the unit of trust, the choice of instance matters more than the choice of app. Before signing up, a new user can read the server’s rules, check who runs it and how they are funded, and look at how long it has operated. Stable, transparent servers tend to publish a moderation policy, list the other servers they block, and explain what happens if the administrator steps away. Accounts can usually be moved between servers on the same software, which reduces lock-in, but followers and history do not always transfer cleanly, so a quick look at the export and migration tools is worthwhile.
It also helps to separate the software from the network. Two people on different projects may share a timeline, yet they depend on different codebases, release schedules and maintainers. A security fix in one does not reach the other automatically. Following the release notes of the software a server runs is the simplest way to judge whether it is kept up to date.
Joining, hosting or building
There are three levels of involvement. The easiest is joining an existing server run by a volunteer, club or nonprofit. The second is paying for managed hosting, which removes maintenance but adds a business relationship. The third is running a server yourself: Friendica’s low hardware demands make that realistic, while Mastodon’s documentation includes a full section on preparing a machine and installing from source. Groups that want to own their space can look at the self-hosted community approach, and teams comparing tools beyond social timelines can consult the overview of each community platform. For a wider survey of choices, the page on social network alternatives covers both open and closed options.
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Frequently asked questions
What is the best open source social network?
No single option wins. Mastodon suits short public posts, Friendica suits Facebook-style profiles and groups, Diaspora suits people who like its pod model, and Pixelfed or PeerTube suit photos and video. Because many speak ActivityPub, accounts on different projects can often follow each other.
Is an open source social network free to use?
The software is free to download and run under licences such as the AGPL. Joining a server is often free, although some operators ask for donations or charge fees to cover hosting, moderation and bandwidth.
Can accounts on different networks talk to each other?
Often, yes. Projects using ActivityPub can exchange posts, and Friendica also bridges to Diaspora. Diaspora does not support ActivityPub natively, and Bluesky uses the AT Protocol, so those need bridges or separate accounts.
Is an open source social network private?
It usually collects less data than advertising-funded platforms, but privacy depends on the server administrator, the software configuration and what a user shares. Messages are generally not end-to-end encrypted by default.
