Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
Facebook Messenger - Facebook Messenger is a faster way to message.
StealthChat - StealthChat is Encrypted, Private, Secure Calls and Chats on Android and Apple iOS
Digsby - Tagged makes it easy to meet and socialize with new people through games, shared interests, friend suggestions, browsing profiles, and much more.
Wire - Private & Secure Messenger