HexChat is an IRC chat program. It allows you to join multiple IRC channels (chat rooms) at the same time, talk publicly, private one-on-one conversations etc.
HexChat is based on XChat, but unlike XChat it's completely free for both Windows and Unix-like systems. Since XChat is open source, it's perfectly legal.
Install HexChat in ubuntu
Open the terminal and run the following comamnds
sudo add-apt-repository ppa:gwendal-lebihan-dev/hexchat-stable
sudo apt-get update
sudo apt-get install hexchat