Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Zoom - Zoom unifies cloud video conferencing, simple online meetings, group messaging, and a software-based conference room solution.
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.
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.
Slack - A messaging app for teams who see through the Earth!
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.