Fez is a simple yet good Internet chatting application. The same application can act as the server or client, and the clients connect to the server using the IP address and port (if specified) of the server.
What's new in Fez
Version 1.5 adds the following:
IP addresses can now be bookmarked.
Completely rewritten from the ground up.
New interface. Also, resizeable userlist (can be hidden by dragging all the way to the right.)