We use yard (a ruby gem) to generate code documentation and also static project overviews, runbooks/workflow guidelines, many howtos and troubleshooting guides.
This works well as all changes to documentation are in version control and have to be reviewed.
The tool generates static HTML which makes the deployment of the docs pretty straightforward.
And then Google Docs/Drive for keeping meeting notes or collabarative planning of features. Google Drive makes file management hard somehow, but the search always works.
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