Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Wickr - Wickr is a free end-to-end encrypted text, video, picture and voice messenger with full sender...
TextSecure - Open Source security for mobile devices
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.
QKSMS - QKSMS is a beautiful communication app that offers magical texting experience.