I actually have been looking for something like this. Mainly so I can give some nontechnical people access to edit different parts of a page. This hasn't been easy to set up in drupal or wordpress (without a large learning curve on their parts). I might give Copybar a try and see if it works out for me.
Copybar cofounder here, that is one of our primary use cases. Instances when a CMS fails to address access controls for nontechnical people. Even drupal and wp can seem overwhelming to some. The best thing is Copybar can sit on top of Drupal and Wordpress. If you do end up using it let us know, we'd love to be able to feature some live implementations.