Try https://www.notion.so! It combines docs, wikis, and todos; it's collaborative, and it's beautifully designed. It's perfect for building knowledge bases for teams.
(Disclaimer / I worked there in the past)
(Disclaimer / I worked there in the past)
There's no Linux download, no github, and especially, no server - I stay away from products like that, sorry.
Almost every company uses external services for this sort of thing right now. Google Drive, Confluence, whatever. Notion allows you to export to PDF/Markdown as well.
https://www.notion.so/Export-to-PDF-or-markdown-5406d98f17d2...
However, I work at a large company that has adopted Confluence, so I'm stuck with that for organizational knowledge.
The lack of an Android client might be a blocker, although according to their Twitter, one is only weeks away.