Winpopup LAN Messenger - Winpopup LAN Messenger is a cost-effective Office, Corporate, Enterprise Instant Messaging solution.
BeeBEEP - You can message and share files inside your intranet without a server.
LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
Feem - Share files offline. No servers. No cloud. No limits.
Bopup IM Suite - Organize secure messaging system and communicate instantly via self-hosted IM server.
Squiggle - Squiggle is a free and open-source, peer-to-peer LAN messenger that is lightweight and feature-rich.