A few people on Reddit were having trouble getting their heads around what the Fediverse actually is, so I tried to write a jargon-free ELI5 description. It’s garnered quite a few upvotes over there so I thought I should actually post it onto Fedi as well!
I’ll see if I can make it all easier to understand. This might be a bit long, but I’ll try to keep it as non-technical as I possibly can.
You will naturally be aware that there are many different systems on the internet, run by different companies. And these systems are generally incompatible with one another.
For example, you can’t use GMail to compose and send a post to Twitter. You can’t log on to Facebook and read content from Reddit (unless somebody has copied it there). You can’t watch Youtube videos via Flickr. And so on.
All of this seems obvious - they’re completely different systems. Why on earth SHOULD you be able to interact with them from elsewhere?
A few years ago some people decided that even though this was obvious, it wasn’t the way the internet HAD to be. They developed a protocol (which is just a set of instructions for computer programs to talk to each other over the internet) which they called ActivityPub, and then basically said to software developers “here it is. We think this could be a cool way of getting different systems to interact with each other. See what you can do”.
In the 5 or 6 years since then, lots of software developers HAVE tried to see what they can do with ActivityPub. One well-known example of a system that uses it is Mastodon. It’s a system that is similar to Twitter.
Another couple of ActivityPub systems that are becoming popular right now are Lemmy and KBin. They are Messageboard systems, roughly similar in concept to Reddit.
There are many other ActivityPub systems, for example Pixelfed (which is a bit like Flickr, so for hosting photos), Peertube (yep you guessed it, videos), Friendica (like Facebook) and far too many others to list. Collectively, these systems and any others that use ActivityPub call themselves “the Fediverse”.
OK - so what? These are just wannabe competitors to the big boys: Twitter, Youtube, Reddit, right?
Not right! The magic of ActivityPub and the Fediverse is that they can all interact with each other.
So you can log on to Mastodon and subscribe to Lemmy groups. That would be like logging on to Twitter and subbing to your favourite subreddit. And then being able to read the posts from that subreddit right there in Twitter.
You can log on to KBin and follow users on Peertube. Imagine being able to follow and view content from your favourite Youtube streams from right here in Reddit.
That’s the real beauty of the Fediverse - every system knows how to talk to every other one. The other clever bit about it is that because ActivityPub is a publicly-defined protocol, no one company can own it and take it over. It’s almost impossible for a billionaire like Elon Musk to take over Mastodon, or for Lemmy admins to decide to shut out third-party APIs. Because the system has been built from the very beginning to be open, and shared, and communal.