b-org, "base-organisation", is a set of content types for handling a common organisation structures, with departments and employees as groups and users, and projects as collaborative workspaces. It is also the basis for a tutorial and is meant to be extended with lightweight plug-ins for use-case specific metadata and behaviour.
b-org should be usable out-of-the-box, though the real value is in customising it for your own use cases. It is built with extensibility and customisability in mind.
b-org is also the subject of an extensive tutorial about developing content types for Plone 2.5 using Zope 3 technologies alongside Archetypes and more familiar tools.
No stable release available yet.