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.
22 Alternatives To WhatsApp
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.
Viber
Free and secure calls and messages to anyone, anywhere. Keep your conversations going no matter where you are.
Zoom
Zoom unifies cloud video conferencing, simple online meetings, group messaging, and a software-based conference room solution.