Dialogflow - Conversational UX Platform. (ex API.ai)
Chatfuel - Chatfuel is the best bot platform for creating an AI chatbot on Facebook.
Api.ai - Api.
Landbot - An intuitive no-code conversational apps builder that combines the benefits of conversational interface with rich UI elements.
Messenger Platform - Discovery, chat extensions, and richer experiences
ChatBot - Easy to use chatbot platform for business