Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Seald - Keep your conversations secure, everywhere.
StealthChat - StealthChat is Encrypted, Private, Secure Calls and Chats on Android and Apple iOS
Crypho - End-to-end-encrypted messaging and file sharing
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
Spike - Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.