Seald - Keep your conversations secure, everywhere.
Chadder - Encrypted messaging app
Keybase Chat - End-to-end encrypted chat built into Keybase
Crypho - End-to-end-encrypted messaging and file sharing
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.