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.
Empathy - Apps/Empathy - GNOME Wiki!
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Psi-IM - Psi-IM is a messaging program that is designed for the XMPP network.
Cotap - Cotap is a simple, secure mobile messaging app for fast, easy workplace communication.
Gajim - Full featured and easy to use Jabber client