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, which, while independently hosted, can communicate with each other.
On different servers (technically instances), users can create so-called identities. These identities can communicate across the boundaries of the instances because the software running on the servers supports one or more communication protocols that follow an open standard. As identities on the Fediverse, users can post text and other media, or 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). A key distinguishing feature of the Fediverse is decentralization. There is no central authority that controls or determines what is acceptable as each instance is independent.
But you're probably here for more specific information.
Outside of the Lede, this will probably not apply unless you're a weeb.
Lede
The first thing to consider is to unlearn traditional centralized social media design: Fediverse instances can probably be paralleled to email (Multiple servers, unrelated to each other, yet can communicate interchangeably), but in the form of a generallly Twitter-like social media. They are very often hosted by completely random individuals like you and me
Generally, you can join any instance and follow me and others "remotely" from your own home instance to see our posts on your timeline
You usually have incredibly powerful control of your experience: migrating accounts between instances that literally bring your followers with you, backing up who you follow to be used on multiple accounts (or in case of a bad day), and granular notification control compared to sites like Twitter to isolate ones you particularly want to see or care for
Note: To avoid confusion, be aware that many of the more popular instances (Misskey, Mastodon, etc) happen to be named off the same software they're built from as their software engineers usually create the first instances centered around them. Unless the context is very explicitly referring to this software (e.g. "A Misskey instance"), you can probably assume the conversation is about a specific website/instance
Random Instance information
Baraag: The largest English-dominant art instance that touts almost complete artistic freedom, and my original Fediverse home. Quite a few instances block them for contentious content on it. I've since moved away from it, but I still appreciate and have immense respect for what the admin's done for artists like me. At the time of writing, their sign-ups are limited with occasional invite codes floating around
Aethy: A recent western-oriented art platform in a similar vein to Baraag, they take a strong stance against hate/harassment by suspending many instances for unsavory users that I've come find are the more 4chan/shitposter types. I have mixed feelings about it, but if it's your tea, go for it
Pawoo: The largest and probably oldest Japanese-dominant art instance that touts almost complete freedom. Though, I feel it lacks moderation these days
Misskey.io: A recent thriving arrival to fediverse conscious, it's effectively become Japanese artist's own Baraag by hosting suspended ex-Twitter users, it's community is almost exclusively Japanese. Either for cultural or bandwidth reasons, they have become a bit closed off
rkgk.moe: This is an "individually ran" Misskey instance by Redi that I'm now headquartering on.
Unless federation is disabled, you can remotely follow me from Misskey(.io), Baraag, Pawoo, or other instances! Just search my name on the instance's search, or some allow you to put my @ in the url with the domain, like so:
There are many, many more, thousands of which are floating around unknown to many people, and huge ones not worth listing because of their harsh nature against my art. As such I find all of the above to be most relevant to my subject matter as an R18 anime-styled and lolicon-adjacent artist
"Which one should I join?"
I would recommend approaching this from top-down decision making:
If you can't make your own: try joining one of someone you trust or know. If you don't know anyone (as is likely), then join one whose administration tries to stay hands off of policing content, such as Pawoo or Baraag at the time of writing this. You have other options, of course, such as rkgk.moe, headpat.cafe, varishangout, Poast, gameliberty.club, or various others as you discover them. They don't need to be explicitly art related to be worth joining, and many of them tend to have very obvious political leanings, but there's probably a place for everyone, and if not... that's the beauty of the Fediverse: Just make your own
What you want as a viewer and artist alike, is a sweet spot that can interact with as much of the Fediverse as possible, as the unification of all smaller instances creates the healthy social ecosystem that Activityhub offers, unless you don't mind being split up between many accounts. This might be the biggest issue with finding a place to start up, but I know instances such as Baraag have fairly strong principles to be as accepting as possible despite, and at least at the time of writing this, are able to federate (interact) with the bigger Japanese artist instances as well
On many instances, you should be able to check who they "federate" with to see if an instance you want to interact with is blocked/suspended (such as the various art ones above). If not, you can attempt to search for a user with "@user@instance" in the searchbar of your instance. If you struggle to locate them or follow them, it might indicate being blocked by your admin, though some instances outright let you see their federation status
Though, in tl;dr, maybe just default to Pawoo if you want to go somewhere that has already established itself and is somewhat stable. Though, if you like Redi's art and want to be around more of it, and desire to be around a generally balanced mix of art both SFW and NSFW, or are just a lurker, I think joining me on rkgk will be fine
P.S.
Fediverse instances are a little daunting at first, and their general lack of algorithms and sometimes scuffed communication between instances make things more "manual" sometimes, but I genuinely think decentralization is the future as social media giants continue to creak under their own weight. Artists are quickly finding themselves with less and less places to share their work without moderation or social issues, and the Fediverse offers safe havens for many of them to create without worry. I recommend exploring the options of wherever you might join to see the full extent of the power you have over your own social media experience in these ecosystems
Remember, you have migratory and following backup abilities on most instances! You do not need to reset every time you move, if you wanna pick up your stuff and move to one that sounds more enticing, use these tools to your advantage to make it as painless as possible! In the moves I've experimented with across multiple softwares, I've found that reposting my art is the (only) consistent thing I need to redo. I have used the migration function multiple times in order to consolidate my following on rkgk, for example
An elephant in the room: moderation on these is usually handled by humans and volunteered, and sometimes is so poor it's virtually non-existent, the culture of auto-moderation and brigading reports to suspend people before you even see them does not exist. Block and mute, and be prepared to see things you do not want to see... which leads me to an extremely important tip...
Don't look at the federated/worldwide timeline, and probably not local either for any popular instance. It's a functional parallel to Elden Ring's primeval current. If you could see Twitter, Facebook, etc's equivalent you would probably heave at the amount of actual illegal things that flow in plain sight across all social media from botting of bad actors or otherwise. You have to intentionally insulate yourself, rather than let the platform do it for you; smaller instances tend to handle that better
