When I was using MS Windows, I found a nice LAN (Local Area Network) Messenger application which can be used to chat and transfer files to other users on the same network. But unfortunately the application is not free. But when I switch to Linux (Ubuntu), I found the similar application called iptux. iptux is a powerful, simple LAN messenger for Linux. The interface of iptux is similar to pidgin (internet messenger). But iptux cannot be used to communicate with other users via internet.
Install iptux on Ubuntu 12.10
sudo apt-get install iptux
Now you must install iptux on other Linux machines in order to chat or send files. All connected users will be listed on the iptux window.