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 via GtkSourceView, a group chat, smart undo functionality, and it’s not just limited to LAN - it can also be used over the Internet.