I found out about Gobby recently, which is an excellent replacement for online (web-based) collaborative editors for a lot of use-cases.
In my case, I was editing configuration files which included passwords, and I didn’t want those files touching the outside network. With Gobby, I could collaborate with other admins over LAN, with TLS encryption.
The application is multi-platform, released under GPLv2+, has syntax highlighting
GtkSourceView, a group chat, smart undo functionality, and it’s not just
limited to LAN - it can also be used over the Internet.
Let me know what you think about this via email or in the public chatroom.