Can highly recommend outline (https://www.getoutline.com/). You can self-host or opt for the hosted version. Built and maintained by one of the linear devs.
replies(4):
1. Does it support rendering OpenAPI json/yaml?
2. Also it seems like it supports Draw.io via public URL. That's a no go. Can it support draw.io diagrams via attachments?
3. Google drive support is nice. Do you plan on supporting OneDrive as well?
2/3. Not currently but anyone could add support for such things