Dialogflow - Conversational UX Platform. (ex API.ai)
Chatfuel - Chatfuel is the best bot platform for creating an AI chatbot on Facebook.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Landbot - An intuitive no-code conversational apps builder that combines the benefits of conversational interface with rich UI elements.
Botkit - Botkit is an open source developer tool for building chat bots, apps and custom integrations for major messaging platforms.
ChatBot - Easy to use chatbot platform for business