Shared Documentation

How should a system of shared documentation work for us?  What do we need it to do for us? 

Not exactly "shared" docs per-se, this is really "collaborative" documentation -- but the "C" word has acquired an unfortuante connotation over the years.  But that's exactly what we're talking about -- collaboration: sharing of information, and also communication, of that information.

The system for shared documentation:

• Must allow a default modifyable by anyone in the group.
• Must provide automatic notification (eg. email, RSS) to group upon addition/deletion/edits of content.
• Must provide method(s) for automatic notification (eg. email) to users when a document they have created or edited has been modified by someone else.
  
• Must provide automatic attribution of edits, ie recording and displaying who edited the documention, when, and what did they change.
  
• Must provide automatic archiving of changes, allowing rollbacks/revert/undo.
• Should allow author to opt to restrict modification to self-only rather than always allowing group modification.