What options are left for self-hosted chat systems with comparable features? We've been using self-hosted Hipchat at our company and there is zero chance we will ever use a cloud solution.
* Rocket.chat https://rocket.chat/
* Mattermost https://mattermost.com/
* Riot/Matrix https://riot.im/
And XMPP is not completely dead, depends on what you mean "comparable features".
When did you last try Zulip on Android? I agree it was pretty much unusable in 2017, but everyone who actively uses it agrees it's improved a lot in recent months (I use it every single day, and have a good experience using it to get my work done). The mobile apps remain our top engineering focus area, since they're certainly far behind the desktop experience's level of polish, but we've generally stopped hearing new users describe them as "unusable".
I should also mention that Zulip's threading model makes the experience of replying to a conversation when you get back to your computer feel great, which isn't true for any other chat tool. You don't have to be glued to your keyboard/phone in order to communicate effectively or avoid missing out on participating in important conversations, and I can't emphasize enough how much better this makes life.
That doesn't eliminate the value of mobile (as I said, this is our top focus area right now), but it's a big part of why people love Zulip today, despite the mobile experience being way behind the desktop experience.
* Self-hosted (simple web application), a Docker image is available, Debian package incoming
* Chatrooms and one to one chat with file sharing, embeded pictures, administration, discoverability, message editing, archives management, synchronisation between devices
* Post publication in Communities and personnal accounts
* Compatible with XMPP transports and services like Biboumi to bridge it with IRC
* Responsive so it fit on your desktop and your mobile (the UI is also fully in sync between your devices)
* Video-conferencing (one to one)
* and many other things…
You can check it on https://movim.eu/ and give it a try :)
P.S.: I'm the maintainer of the project
--Hipchat onprem user
It's pretty simple to adjust permissions using Riot - I haven't tried it with the other clients, though.