Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
FluffyChat - Open. Nonprofit. Cute ?
WeChat - WeChat is a complete mobile communication and private social networking app.
Olvid - The most secure messaging app in the world.
Viber - Free and secure calls and messages to anyone, anywhere. Keep your conversations going no matter where you are.
Molly (Signal fork) - Molly is an independent Signal fork for Android