Microsoft Bot Framework - Framework to build and connect intelligent bots.
Chatfuel - Chatfuel is the best bot platform for creating an AI chatbot on Facebook.
ChatBot - Easy to use chatbot platform for business
Landbot - An intuitive no-code conversational apps builder that combines the benefits of conversational interface with rich UI elements.
Amazon Lex - Harness the power behind Amazon Alexa for your own conversational apps.
Dialogflow - Conversational UX Platform. (ex API.ai)