Sender

Sender is a very very small Windows network messaging utility.

If you use "net send" for sending short messages across your network, this tool is for you. Sender is a replacement to "net send" for sending messages and also gives you the power to handle incoming messages. There is no need to stop the standard Windows Messenger service (see note below).

To send messages Sender uses nearly the same procedure as "net.exe" is using. Multiple recipient send is also supported (names must be separated with spaces).
To receive messages it just intercepts Messenger service's windows and process the information.