Posting threads and topics only visible by specific group

[rimann]

Does anyone know if this is possible with the stock tools or if there is currently a plugin to acheive this?

The Goal:
The ability to select visibility of certain posts, for example an announcement, visible only to those in a specific group. Or a way to create categories only available to members of a specific group.

[PitaJ]

You can already create a category only visible to a certain group by creating such a group and selecting the privileges in the ACP.