Whiteboard App?

Wondering if anyone uses or knows of something like what I am looking for.

Need an app for PC (Mac compatability would be nice) that is essentially an inter-office messageboard. I found Noodleboard as a Mac only option (and its no longer available). I am trying to just have a place on people's desktop/app where a general message can be left. I.E. "We are sold out widgets start selling trinkets!". Messages can be edit/add/deleted (within the network/group) by all users.

Does such a thing exist? I tried searching google for apps/programs but couldn't get any good keywords to go on as everything was too general.

Any WW's there with a decent solution?