Tox - Send messages, files, create groups and make Tox to Tox audio and video calls. Securely.
FluffyChat - Open. Nonprofit. Cute ?
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Olvid - The most secure messaging app in the world.
uTox - µTox is the lightweight client with minimal dependencies; it not only looks pretty, it runs...
Molly (Signal fork) - Molly is an independent Signal fork for Android