FluffyChat - Open. Nonprofit. Cute ?
Molly (Signal fork) - Molly is an independent Signal fork for Android
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
TeleGuard - TeleGuard is a secure messenger that makes it store that your data or chats are not stored while collaborating or communicating with partners and friends.
aTalk - An encrypted instant messaging with video call and GPS features for android.
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.