BuddyPress.org

@Tapaninaho:

Check out Peter Anselmo’s Group Documents plugin: https://wordpress.org/extend/plugins/buddypress-group-documents/

Peter does great work, and this plugin might get you very, very close to what you need. It provides a document repository for groups, allows uploaded files to be categorized and provides a backend management tool to determine allowable file types – among other features.