I personally use BookStack (http://bookstackapp.com) as my knowledge base. It has many features like third party authentication and draw.io (now diagrams.net). Maybe HedgeDoc is more (https://hedgedoc.org/) what you are looking for.
I haven't tried it, but there was an article in the latest Linux Magazine about https://hedgedoc.org/ -- perhaps check it out?
> While HedgeDoc is reminiscent of Google Docs and Etherpad, HedgeDoc has the ability to show both the actual Markdown source code and the HTML web page preview.
This comment is of course formatted with Markdown :-)
Sync files, but also asymmetrically: Have you considered a Samba share?
A Talk equivalent: Jitsi?
Doc collab: I've been using Etherpad for this, but I'm considering switching to HedgeDoc because of my experience with this now fixed bug which leads me to suspect that sqlite + etherpad don't mix terribly well.