Separation of privilege. You already know all this stuff. Access control lists and capabilities for more flexible protection. Detailed examples of descriptor-based protection systems. Thus capabilities can be very efficient, since access check need only be done at initial bind time.
Disadvantage is that revocation and propagation control gets really hard.
Access control lists. Objects have an ACL associated with them that says who can get what access to the object. Revocation, etc. get easy, but performance suffers since the heavy-weight access check is performed at every access. Allows user-specified programmable access controls. Most systems didn't provide much security, or only recently began worrying about protection.