Internal Chat system.

Is there a plugin that allows you to communicate with the people writing your articles?

For example I want to be able to communicate with my Administrators,Editors, Authors, and Contributors inside the website using a instant messaging-like chartroom system. Instead of trying to email them or call them on there phone, I would like to instant message them if they are online or offline.

Or if there is a plugin that allows private messaging to other users. If there is I am not aware how to use it.