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).