FluffyChat - Open. Nonprofit. Cute ?
Olvid - The most secure messaging app in the world.
Molly (Signal fork) - Molly is an independent Signal fork for Android
aTalk - An encrypted instant messaging with video call and GPS features for android.
NYNJA - NYNJA is an all-in-one communications tool that comes with real-time support to share files and chat.
Hype by Opera - Hype is a chat service made into the Opera Mini browser that allows you to chat, share, and browse different kinds of stuff in a single application.