This is a stealth chat, with which you can send messages to another computer who has started the xMessenger server (possibly stealthily in background). The connection uses TCP (port 11112 by default). You just need to know the IP address.
Run xMessenger server on the target computer
Run xMessenger client and connect it to the server by entering the IP address
Make sure that TCP port 11112 (by default) is open
Send few messages in a message box or in the system tray
You can set up some elements, like the priority, the icon, and you can give the right of reply