Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Dialogflow - Conversational UX Platform. (ex API.ai)
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Botpress - Open-source platform for developers to build high-quality digital assistants
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Messenger Platform - Discovery, chat extensions, and richer experiences