Looking for a recommendation for producing software documentation for three different audiences: internal, partners, and open to the web

Internal: for our software development team only so partners or external people can't see it. Ideally still collaborative and on the web

Partners: for other entities working closely with us. It would basically be a subset of Internal with read-only permissions.

Web: for anyone to look at. A subset of the above where anyone can search through with a browser.

I've frankly never handled documentation before so I'm out of my element. In the next year or so I'd expect a few hundred pages of documentation in there.

Any recommendations?