We use Pydio
Tech-Party File Sharing
There's always a file someone needs, or something we always use and can't find, so we made our own file sharing section.
Pydio seems to be a great solution. Again, we chose Pydio because it is part of the free suite from Godaddy and had no special setup or conflicts with other apps.
Right now it looks like we have to set up users individually, if you would like access or have an inkling to administrate a file section, contact us.