Ask HN: Recommendations for internal docs / knowledge-base?

Digital Agency; we've got an incredible amount of docs scattered between google drive, emails, confluence, repo wiki's and readme's, trello/aha, and inside people's heads - just thought I'd see if folks have any advice / recommendations on tools / processes to get it all together in one place, and make it more uniform / easier to search / use - as currently it's still easier just to grab the "knowledge" person and pick their brain (with the detriment of disturbing them during their current work sprint).

I'm more concerned with "internal" stuff; such as guides to a platform, who to notify when X happens, or who'd be the best person to talk to about Y platform etc - essentially a company handbook of sorts, rather than client related stuff such as specs / scope of works etc.