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.
MyChat - Secure instant messenger for any network
Squiggle - Squiggle is a free and open-source, peer-to-peer LAN messenger that is lightweight and feature-rich.
BORGChat - BORGChat is a LAN messaging software program.
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.