Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Easy Message - Easy Message app comes up with features to help users in effortlessly sending text messages to a phone number, which is not in the contact list.
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
Message Peeping Tom - Message Peeping Tom is an app by HSTAR, offers features that let you read your messages without giving the read report to the sender.
StealthChat - StealthChat is Encrypted, Private, Secure Calls and Chats on Android and Apple iOS
Wire - Private & Secure Messenger