WinMessenger

WinMessenger is a replacement for the standard Messenger Service, ‘net send’, and WinPopup tools. It is an easy to use program that allows you to send and receive messages from computer to computer in real-time without using dedicated servers.

It works over any network protocol (TCP/IP, IPX/SPX, NetBEUI, etc.), it is easy to deploy and it does not require computer knowledge or special configuration