I really don't want to mention our product again on the same page, but you mentioned Drupal, which is what we built our, I guess I have to say, Sharepoint alternative: OfficeMedium ( I won't spam another link on the same page )
I think we're on the same page though: Simplicity is key.
Does OfficeMedium have samba sharing or similar feature so documents can be added without uploading via a web interface? I've been looking for a good content management system for my job. Alfresco ( http://www.alfresco.com/ ) seems to present itself as a shared drive on user's PC but it doesn't do events + calendaring that OfficeMedium seems to support.
I think we're on the same page though: Simplicity is key.
Drupal is the best...