[dexwiz]

I think Salesforce Chatter is a good implementation of this. Basically any object in Salesforce (cases, contacts, any custom object like bug reports) has a chatter feed attached to it where people can post and reply. Its got functional @mentions and file attachment. There are also generic Group feeds for communication with a group of people not relating to a specific object.

However, it's more of a comment thread than a real time chat application. You have to refresh the page to see new updates. Also since there is no where to "hang out," it's hard to talk to someone directly. Sometimes you post and have to @mention three of four groups to find someone to respond.