ChatSecure - ChatSecure is a free and open source messaging app that features OTR encryption over XMPP.
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.
ChatIW - Meet and Chat with new friends around the world.
Kandan - Open Source private chat server. Your own private Chat server in minutes, plus additional features.
Bit Chat - Technitium Bit Chat is a secure, peer-to-peer (p2p), open source instant messenger that is designed to provide end-to-end encryption for privacy using strong cryptography.
Chatib - Chatib is an online chat room where you can meet and chat with new people, make them friends, or even data them online.