From Shirouzu Hiroaki:
IP Messenger is an application to chat inside your Local Area Network (LAN). This is a pop up style LAN Messenger for multi platforms. It is based on TCP/IP (UDP) and does not require server machine. Features include serverless message communication, fast file or folder transfer, image embedded message and desktop (area specified) capture, and message encryption (RSA2048bit + AES256bit) and sign or verify (PKCS#1-v1_5).
Very simple little chat program works perfectly on a home network.
Gives a small popup alert when new message arrives.
Chat window lists all members of home network who are currently available.
You can drag and drop files or photos into the chat window to send, or just type messages back and forth.
More people can join the conversation if you allow it.
You can change the font in your own chat window but it doesn't show up that way in the other person's chat window (at least, we haven't been able to make it work that way so far).
Does not support video chat or voice chat as far as i can tell.
If you have a home network or office network and want to send and receive messages or transfer files WITHOUT going on the internet this is a great little program. It's small, it's free, and simple. And, it's not a resource hog on your computer. These days there really is no privacy on the internet at all, so keep your local network/LAN conversations more private by using this.