Using Signal, you can communicate instantly while avoiding SMS fees, create groups so that you can chat in real time with all your friends at once, and share media all with complete privacy. The server never has access to any of your communication and never stores any of your data.

https://whispersystems.org/ https://www.signal.org/
https://github.com/WhisperSystems https://github.com/signalapp

Get Signal

Or install app on mobile:

https://www.whatsapp.com/ - WhatsApp

The Signal Protocol, designed by Open Whisper Systems, is the basis for WhatsApp’s end-to-end encryption. This end-to-end encryption protocol is designed to prevent third parties and WhatsApp from having plaintext access to messages or calls. What’s more, even if encryption keys from a user’s device are ever physically compromised, they cannot be used to go back in time to decrypt previously transmitted messages.

https://www.whatsapp.com/security/WhatsApp-Security-Whitepaper.pdf

https://go.skype.com/privateconversations - Skype

In collaboration with Signal, Microsoft is introducing a Private Conversations feature in Skype, powered by Signal Protocol.

https://signal.org/blog/skype-partnership/

https://googleblog.blogspot.com/2016/05/allo-duo-apps-messaging-video.html - Allo

We’re excited to partner with Google on the private communication features of their new smart messaging app, Allo. We’ve been collaborating together on the integration of Signal Protocol into Allo, which will bring all of Signal Protocol’s strong encryption properties to Allo’s incognito mode.

https://signal.org/blog/allo/