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...
Softros LAN messenger - LAN messenger for an internal office chat for home or business users. It does not require a server and is very easy to install and use. It supports personal chats, group chats, message brodcasting, files transfer and remote desktop access.
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.
Winpopup LAN Messenger - Winpopup LAN Messenger is a cost-effective Office, Corporate, Enterprise Instant Messaging solution.