Confluence and/or Google drive or similar. I prefer confluence over G drive. I have also seen some nice examples of documentation on Notion https://www.notion.so, but I don’t know how good it is for a company.
My criteria for selecting a source:
1 - Has plenty of tools/options for formatting and visualization.
2 - Excellent search capabilities.
3 - Can give structure to documents like table of contents, footnotes, attachments etc.
4 - Can easily allow me to organize documents.
5 - Is pretty to read.
6 - Supports code formatting.
7 - Allows users to give feedback easily easily & stores them neatly.
8 - Tracks changes like version control & can notify people when something is changed.
9 - Can play content (e.g videos, pdf etc.) without having to download and play.