: Most systems utilize either a Client-Server model, where a central server handles message broadcasting, or a Server-less (P2P) model for direct communication.
If you are looking to download and study existing implementations, several free and open-source options are widely cited:
Secure, server-less, and supports group chats and file sharing. TrueConf Info
Server-less, cross-platform (Windows, Mac, Linux), file transfer, and message logging. Download
LAN (Local Area Network) chat software enables real-time communication within a closed network, often without requiring a server or an internet connection. These applications are frequently the subject of academic papers and project reports due to their use of and TCP/IP protocols to manage peer-to-peer or client-server interactions. Core Concepts in LAN Chat Papers
A free, open-source LAN messenger that is easy to deploy without complex configuration. GitHub
Popular for office environments; supports remote desktop and group rooms (Free trial/version often available). Microsoft Store Key Research Resources