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.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Keybase Chat - End-to-end encrypted chat built into Keybase
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Crypho - End-to-end-encrypted messaging and file sharing