topic of the week

Hi there. I’m building a multiple contributor blog, and want to be able to have a ‘topic of the week’, or something similar. Though not actually time dependant. Just a ‘current topic’.

I initially thought to use the categories system, but would need a way of limiting the contributors to posting under a single category, while the other categories remain in an archive.

I have searched for some time, but can’t find anything in the forums or plugins directory to get me any closer to this. Can anyone point me in a sensible direction?