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.
Tox - Send messages, files, create groups and make Tox to Tox audio and video calls. Securely.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Zulip - Chat for distributed teams. Zulip combines the immediacy of real-time chat with an email threading model. With Zulip, you can catch up on important conversations while ignoring irrelevant ones.
uTox - µTox is the lightweight client with minimal dependencies; it not only looks pretty, it runs...