Keybase Chat - End-to-end encrypted chat built into Keybase
Dialogflow - Conversational UX Platform. (ex API.ai)
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.
Seald - Keep your conversations secure, everywhere.
Botkit - Botkit is an open source developer tool for building chat bots, apps and custom integrations for major messaging platforms.