internal communication among blog authors

Does anyone know of a plugin for an easy way of communicating among blog authors? I am looking for something that will preferably show up on the dashboard and be completely in house. A forum or internal miniblog or something? I don’t want to use the private Notes plugin because we need to discuss stuff as a group.

The various plugins for hiding posts from different roles don’t seem all that good either since they still display a “locked” post to non-registered users.