Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
qTox - A Qt graphical user interface for Tox.
Tox - Send messages, files, create groups and make Tox to Tox audio and video calls. Securely.
uTox - µTox is the lightweight client with minimal dependencies; it not only looks pretty, it runs...
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.