Dashboard Screen Options for Collaboration

Just wondering if anyone has any suggestions vis a vis plugins that would go into the dashboard of wordpress that will help to facilitate collaboration between authors. Are there any plugins that will add widgets like this to the dashboard?

The simplest example I can think of would be a widget that would appear only in the dashboard (for registered users) that I could write announcements on.

I haven’t been able to find anything that’s dashboard specific. Any suggestions?

Thanks