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.
MyChat - Secure instant messenger for any network
BORGChat - BORGChat is a LAN messaging software program.
RealPopup.it - A network messaging application that's feature-rich yet easy-to-use and won't cost you a fortune, RealPopup LAN chat offers fast, stable messaging across your local network. No application server required, just install on your PC and start messaging!
AChat - AChat enables you to chat on your local network (LAN). But you can also share entire directories or send specific files, show images to other users and send messages even to users who are currently offline. Everything with full Unicode support.