I'm probably going to sound old and grumpy but I've been using Slack for work for 5 years now, plus I've briefly checked out Mattermost and Riot/Matrix, and I've yet to be convinced that they couldn't just be replaced by a fancy IRC client that supports markdown, autoloads images n' stuff.
While they may offer some higher-ups some benefits I don't see anything I'd miss if we moved to IRC, quite the contrary — I could maybe even reclaim some of my RAM and get to choose a client to my preference (which is not an Electron app).
The only reason I haven't advocated replacing Slack with IRC is it lacks a sensible way of keeping history. Everyone either has to keep their client running and connected all the time (usually this is only feasible with tmux/screen on a server), rely on bouncer hacks, or something like IRCCloud which maintains the connection for you but is proprietary and not self-hostable.
I use https://riot.im for IRC for some channels. It stays connected, keeps archives, etc.
For small communities, I recommend Mattermost or Rocket Chat. I used to be a die-hard fan of irssi inside tmux, but seeing how tiny usability issues can really cause adoption issues, I wouldn't even recommend riot.im to less technical people.
>I've yet to be convinced that they couldn't just be replaced by a fancy IRC client that supports markdown, autoloads images n' stuff.
I've heard this so many times I'm surprised nobody has done it yet.
You'd need a client-proxy, or server extension to detect idle desktop clients so you can route messages to a mobile device, for maximum "life work balance."
While they may offer some higher-ups some benefits I don't see anything I'd miss if we moved to IRC, quite the contrary — I could maybe even reclaim some of my RAM and get to choose a client to my preference (which is not an Electron app).