Jabber!

And why you should use it...

catgirl! now you have to use it!!

jokes aside, let's start with a quick rundown on what Jabber is.
Jabber (or XMPP, but I prefer calling it Jabber), is a Free as in Freedom (learn more about Free Software here) messaging standard that first began development in 1999. It has a number of useful features, like being decentralized, freedom-respecting, extendable, and good for privacy. I'll explain why Jabber is a good solution for IM for just about everyone, as well as further explain its features and try to answer some FAQs.
Please note that Jabber has nothing to do with the software of the same name created by Cisco.

Jabber, first and foremost, lets you be free and sovereign; you can run your own Jabber server, use one that a friend runs, or use a public one, and all of these servers can talk to each other through a method of decentralization called Federation. If you're familiar with email, then you know how federation works: servers that speak in the Jabber standard are able to communicate with each other, letting their users send messages to each other. In fact, Jabber IDs look very much like emails; for example, mine is "gs@greatsword.xyz". This means that Jabber is not owned by any one party, and it is impossible to censor or enshittify. It is perfect if you want to speak freely.

Privacy is also another useful feature of Jabber. Because of its extensible design, developers are able to improve upon it, and one such improvement is end to end encryption. The current-day encryption system of Jabber is called OMEMO, and it is based on Signal's encryption system. It is very set-and-forget, you just turn it on and all of your DMs and private group chats are secure from prying eyes! Not even your server operator can read your messages. Every major platform has a client that supports the OMEMO system, many of which have OMEMO on by default. End to end encryption is uniquely useful in a decentralized system like Jabber, since it means it is harder to backdoor and control.

Jabber is a very lightweight protocol. It is very cheap and low maintenance to run a Jabber server, and the standard itself is light on bandwidth. Jabber works comfortably over throttled data plans, spotty internet connections, and its fast enough that geographical distance is hardly noticed at all. In terms of running a Jabber server, very cheap cloud hosting plans or old laptops can easily be used to run a Jabber server, meaning just about anyone with technical know-how can run one. Even if you don't run a server nor do you know anyone who does, this means that there are more public servers to choose from, overall making the open network a much more decentralized. There are also a number of simplistic Jabber clients out there for those who are using extremely old/low power computers or phones. There's even a Jabber client that works on a few button phones / feature phones!

Jabber is easy to set up for both users and server operators. Setting up something like Prosody or Ejabberd is not much more difficult than setting up something like a Minecraft server. It's a great way to learn sysadmin basics if you don't have that skill already (and it is is a very enjoyable and useful skill to have). In terms of being an end-user of a Jabber server, pretty much all clients look and behave like normal chat clients you are probably already familiar with. I might make a guide in the future on how I like to set up Ejabberd, but here is an excellent guide on how to set up Prosody.

Jabber is trustworthy! If you're using a fren's server or you yourself are the server operator, then you can trust that your data won't be sold to antisocial adtech companies. In terms of most public servers, it is very hard to get away with being shitty on the network, and most server operators would never dream of it. In terms of the software, all of the major Jabber servers and clients are Free Software, so the code can be audited and we can be sure no one is doing anything evil.

The X in XMPP stands for eXtensible. Jabber has been continuously improved over the past 25+ years, thanks to the aforementioned extendable design. Many features that did not exist in Jabber were later added as time went on, and many of these features end up in many different clients thanks to the standards process, so it is a living and improving system. If you're a tinkerer and want to experiment with real-time communication, or you're just an end user who wants to benefit from a living breathing protocol, Jabber is a great system to learn with!

Jabber servers are flexible. If you're a technical person, then Jabber servers like Prosody and Ejabberd will be a delight to use and set up; you can change just about any feature, disable or modify certain features that you don't need, and you can control what goes on the server. Both Prosody and Ejabberd have plenty of user-management features too, which makes it a great fit for the technical person who seeks to get their less technical friends and family on a safe server immune to spam, scams, and other undesirable behaviour. No need to worry about losing passwords when you can just reset the passwords yourself!

There is not much spam on the Jabber network. Because it is impossible to know of every single Jabber server being run out there, spammers simply cannot discover everyone on the network easily. Jabber also has some features to further prevent spam, like not revealing JIDs in public rooms (this means users cannot direct message you just because you're in a chat-room with them), or, running a private server that does not speak with any other server.

Jabber is a fantastic alternative to SMS! (this is for my NA frens) Jabber is leagues ahead of SMS for a number of reasons: it has, at the very least, TLS encryption (the standard security all websites on the internet have), where SMS has no security at all! Your messages are completely out in the open for anyone to read! You can use Jabber with a normal internet connection, and there are no long distance charges. Because of its lightweight nature, it won't consume much of your data at all. Jabber has the ability to send any attachment, and 100% of servers have larger size limits than MMS. Finally, since Jabber is standard across Android and iOS, you can be sure your group chats work! (but seriously, even if you don't use Jabber, leave SMS in the dust for literally anything else!!!)
oh and in case you can't leave behind SMS, consider subscribing to JMP.chat! This is a Canadian paid service on the Jabber network that lets you purchase a telephone number and use that to text any phone number in the world! Also, since Jabber lets you log into one account with many devices, you can use that phone number on your phone, tablet, and computer! Jabber does SMS better than SMS!

Some things to know before using Jabber

There are, of course, some caveats to using Jabber.

Jabber's network effect is not as strong. There are many Jabber users out there, it's not difficult to meet new people on Jabber, but the chance of meeting a random person on the Internet or in real life who uses Jabber is very low. You may be the one who introduces Jabber to someone, not the other way 'round! There exists Gateways (or Bridges) for Jabber: server software that lets a user control an account on a platform such as Discord through their Jabber account. Gateways are only a patchwork solution, as there are plenty of usability problems with them, and they require that you run your own server. Using Gateways on certain services can even get you banned! Furthermore, from personal experience, Gateways often do not lead to people switching to Jabber, and is mainly just for protecting yourself against social suicide.

There is no one client to rule them all! Every major platform has a decent enough Jabber client that supports most modern features, but they are all developed by different organizations, they have some differences in look and operation (most of these differences are visual, not functional), and they are all called something different (i.e. Gajim for PC, Conversations for Android, Monal for iOS, ConverseJS for web.) This may be off-putting for some people, as there is not one single app you can just tell someone to use. There are some differences in features between them, but none of them have any glaring incompatibilities between each other. There is a new client being developed by ProcessOne (the company who created Ejabberd) that may change this in the future.

Calling is not ready yet in Jabber. End to end encrypted voice and video calls are a feature in Jabber, but it is not yet fully developed, and it is not supported across all the major clients. Currently, Android's Conversations and iOS's Monal support end to end encrypted calls between two people, and works reasonably well. There is no calling support for any of the clients on Windows, and Dino (a client exclusive to GNU/Linux) has support for voice and video calls, but it is inconsistent with any other client besides Dino. Only Movim and Dino have group calls. None of these clients have the ability to stream your screen to viewers. Simply put, if you heavily use group voice calls, consider using Mumble or Jitsi alongside Jabber. You can reasonably use 1:1 calling on a phone to another user on a phone.

Most Jabber software are developed by volunteers. As is the case with nearly all Free as in Freedom software, one of the major servers and all of the major clients are developed by programmers in their spare free time. For this reason, progress can sometimes be slow in the Jabber world.

Jabber clients lack fun features found in other chat services (games, stickers, emotes, etc), but you might consider this to be a positive if you prefer your chatting experience to be distraction-free.

Because of the way OMEMO security works, message history is lost when you use a new device. Furthermore, most server operators do not store server-side history forever (the average is around 2 weeks to a month). Please do not get too attached to your message history, or back it up regularly!