Run `ssh devzat.hackclub.com` to try it out! The repo is here: https://github.com/quackduck/devzat (golang).
It has markdown and emoji support, DMs, channels, and it can show images too. You can send code, and it gets syntax highlighted (you can change the theme). You can ping people like so: @user and it sends them a \a, which should play an audible sound if the terminal allows it. There's inbuilt games and rainbow names and a lot of other small things I don't remember right now.You might find the auth system interesting: it's based on a hash of ssh pubkey (bans use that and a hash of IP, so it isn't so easy to get around a ban)
Also an interesting issue: bots that go around trying to brute force ssh into random IPs with common usernames. My current solution is banning if rapid successive joins are detected.