I only run documentation for a small team (4 people), so can´t comment on scaling. But after a lot of failed attempts (word document, text files, wiki) for now we settled on MS OneNote... yeah I know... as team leader I was resistant to it. But after noticing my team members had each started their individual notebooks, I thought - what's the point on trying to force them to use something I think is better but that is not working for everyone, when they already found the solution for themselves.

The setup we use is a monolithic MS OneNote notebook stored on MS Sharepoint.

I know this setup is dependent on your shop buying the "expensive MS stuff", but we already had it anyway...

This setup gives us the following "features":

- Everyone can edit at the same time

- Changes are tracked and identifiable by username (you can rewind the file history)

- Editing process is very easy and user friendly (you can drag in files, images etc into your notes, and it just integrates seamlessly. particularly with the rest of the MS Office suite)

- OneNote notebook layout is actually pretty good (horizontal tab based main sections, that can each hold multiple pages of content. these pages can be visually organized in a hierarchy)

- It has good search functionality