The Squiggle application was developed to be a free lan messenger that does not require a server. Just download and run it and you're ready to talk to everyone on your LAN. Squiggle is a lan messenger done right. Server-less LAN Chat software that is easy to use and has a great UI.

Key Features:

Server-less peer to peer LAN chat, No installation required. Just download, unzip and run
Group chat, Broadcast chat and Private chat
Bridge for connecting two LANs across subnets or WAN.
Localized i.e. translated client available in German, French, Arabic and Chinese
Fast (multiple) file transfer
Spell Check, Buzz, Emoticons, Audio Alerts, Tray Popups
Contact groups, Display message, Display Pic, Chat commands, Message aliases
Chat history, Status history
Voice Chat