Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Spike - Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.
blockslack.io - Chat for small teams — encrypted and decentralized
Keybase Chat - End-to-end encrypted chat built into Keybase
Hie Chat - Know what your friends are doing and chat without typing
Seald - Keep your conversations secure, everywhere.