XMPP fills the very important "simple, and gets the job done" niche in this space. I was looking into options for a self-hosted chat service for team development about a year ago, and landed on XMPP. -- I'm happy to entertain suggestions, if I've missed anything, but I don't want any cloud service, and mattermost is bloated as hell.
Well, it doesn't fill anything but was there before XYZ came. Matrix has mostly the same properties (open source, federated). Signal is not federated and WhatApps is neither federated nor open source (but has the most users).
The things that make XMPP unique are very superficial. For a long time, it was the dominant IETF Standard for instant messaging and it has proven that it can adapt to new circumstances (mobile clients), but who cares about such stuff nowadays ;-)
Compared to running your own email server, you just have to solve different problems:
- XMPP has higher uptime requirements (from a user perspective)
- spam is not such a big problem for small installations
I might be biased, but I self-host both XMPP and email, and XMPP is easier. Roughly equivalent in resource usage for a small private server.
Snikket (a project I started) is probably the easiest way to get a modern XMPP setup these days, or (if you're more into system packages than docker) it's pretty straightforward to get up and running with Prosody, this guide being a good indication of the few things to think about beyond "apt install prosody".
> Is this “because I can” or does XMPP fill a niche in modern text chat?
Not only text chat, but also audio/video calls, file transfer. And not sure if it is exactly a "niche", but it is a standard for a federated IM, quite widely supported. Probably the only comparable alternative now is Matrix, but that comes with a bunch of downsides.
> This feels like a step beyond running your own email server.
Running both XMPP and mail servers, I find that an XMPP server setup is easier: there are fewer components, less spam, fewer restrictions on federation; I think you can run it fine even with a residential ISP unless there is a NAT. Not that email setup is particularly hard though.
Hosted secure chat is still a very important niche. Matrix.org is failing so far once you add many users. XMPP fails too, usually, but for different reasons (configuration issues hard to debug, apparrently).