Any page can have live web chat added to it. In the page editor click on the icon and a chat console is added to the page. You can use this to communicate with any other user on that page. Messages are posted live and have a life of one minute after which they are removed. For example:
If you would like to have a web chat that is shared across pages or even your whole wiki, just set the queueName attribute in the edit page to the same value on each page.