Konversation - Konversation is an IRC client which gives you speedy access to Freenode network's channels...
Pidgin - Pidgin is an easy to use and free chat client used by millions. Connect to AIM, MSN, Yahoo, and more chat networks all at once.
Kiwi IRC - A hand-crafted IRC client that you can enjoy. Designed to be used easily and freely.
Trillian - Trillian is a decentralized and federated instant messaging platform that lets your whole company send private and group messages, keep tabs on what co-workers are doing, share files, and much more.
mIRC - mIRC: Internet Relay Chat client
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.