Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Empathy - Apps/Empathy - GNOME Wiki!
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Adium - Adium is a free instant messaging application for Mac OS X that can connect to AIM, MSN, Jabber, Yahoo, and more.
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
IM+ - Chat everywhere! IM+ is the most widely used mobile IM app! Connect all-in-one to MSN, Yahoo!, Goo...