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
blockslack.io - Chat for small teams — encrypted and decentralized
Seald - Keep your conversations secure, everywhere.
Hie Chat - Know what your friends are doing and chat without typing
Hermes - Pandora Client for OS X