Chatfuel - Chatfuel is the best bot platform for creating an AI chatbot on Facebook.
Landbot - An intuitive no-code conversational apps builder that combines the benefits of conversational interface with rich UI elements.
Dialogflow - Conversational UX Platform. (ex API.ai)
ChatBot - Easy to use chatbot platform for business
IBM Watson Assistant - Watson Assistant is an AI assistant for business.
Rasa Core - Rasa Core is a well-designed dialogue engine used to create chatbots.