Squiggle is a free server-less peer to peer LAN messenger.

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.
• Supports localization i.e. you can replace the translation file to use Squiggle in your native language.
• 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

Server-less LAN Chat software that is easy to use and has a nice UI.

http://squiggle.codeplex.com/