Keybase Chat - End-to-end encrypted chat built into Keybase
Dialogflow - Conversational UX Platform. (ex API.ai)
Seald - Keep your conversations secure, everywhere.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Hermes - Pandora Client for OS X
Botpress - Open-source platform for developers to build high-quality digital assistants