Imagine you’re a brand new Mastodon user, looking for a Twitter replacement. You’ve been around for long enough to get a feel for how things work. You’re starting to build a network of followers but some of them are talking about features that you can’t find. You ask them where to find these settings, and they reply “Not everybody in the Fediverse is using Mastodon.” What on earth are they talking about?

Mastodon

You’ve probably already noticed that there is more than one way to use Mastodon. Aside from the having to choose an instance, you also have a range of user interfaces to choose from. You can get in through your instance’s webpage, or you can install one of the dozens of available apps. Each of these options works slightly differently, with it’s own interface and range of extra features. But they all work together – an Ivory user can still read and respond to my posts from Tusky. This isn’t too surprising because they are all designed to work with Mastodon, and the company behind it has made no efforts to lock out 3rd party developers.

Fediverse

But it turns out that you can also connect to people who have accounts that are not on Mastodon. That is because Mastodon is just one software project amongst many which are all designed to work with the Fediverse. Mastodon is biggest of these projects, at the time that this article was written, and so is the most famous. It was built as a replacement for Twitter, although the developers made the decision to tune it more for user safety and privacy instead of data harvesting and advertising profits.

Like Mastodon, many Fediverse projects are built as replacements of large, successful centralized social media products. Friendica, for example, is a good alternative to Facebook, while Peertube is a video sharing platform like YouTube. PixelFed replaces Instagram. Some projects combine features of these services, while others try to create something entirely new. New projects appear all the time. You can find a partial list here, or by asking your favourite web search engine.

ActivityPub

A key feature of the Fediverse is that all services can work together. If your friends are all sharing their photographs on PixelFed, you can still follow them from within Mastodon. In return, they can follow your Mastodon account from within PixelFed. You can do all the usual social media actions on each other’s posts, such as commenting, liking or boosting. Boosting, by the way, is also called retweeting or sharing, depending on which app you’re familiar with. You can even block and report! This interoperability is all made possible by shared protocols.

There are several protocols commonly use on the Fediverse, but the most common is ActivityPub. ActivityPub is an official W3C recommended standard. It is a decentralized social networking protocol, which works on two layers. The first governs how clients communicates with servers to create, update and delete content. The second is a federated protocol allowing servers to communicate with each other, sharing notifications and content. So while Mastodon, PixelFed and the rest might have their own unique interfaces and features, they all do so within the boundaries of ActivityPub. This means that they can all work together. That’s why users of all these services are able to communicate freely as if they were on the same service.

The Fediverse is not limited to ActivityPub though. Other protocols include diaspora, Zot and OStatus. These different protocols are not directly compatible. They are all a part of the same Fediverse though, because of the apps that support them. Some apps support more than one protocol, similar to how your email client works. Most mail clients support both IMAP and POP3 for mail retrieval, despite their radical differences. It’s also possible to create bridge software, that will receive messages from one protocol and retransmit them for another. This provides some limited federation between incompatible networks. Generally speaking the most coherent federated experience is to be found within a single protocol. Multi-protocol apps will allow their users to straddle multiple networks. But so long as intercommunication is possible, they’re all part of the Fediverse.