Out of curiosity, where and how things were documented? And where were important conversations posted?
- https://www.yammer.com/ (is this still a thing? used it like 10 years ago)
- etc...
We also used slack (or equivalent... also used hipchat, and even jabber before that) for ephemeral, one off, non important stuff. And then a lot happens also in READMEs, Merge/Pull Requests, Gitlab issues, helpdesk tickets, etc. Not much use of emails other than for notifications.
At the end of the day everything has a link and things can reference each other.
I think what most companies are missing is a way for employees to "post" and "subscribe" to updates that are interesting for them.