Dialogflow - Conversational UX Platform. (ex API.ai)
Chatfuel - Chatfuel is the best bot platform for creating an AI chatbot on Facebook.
Octane AI - Octane AI offers tools to create a bot and engage customers and audience via messaging.
Gomix - The easiest way to build the app or bot of your dreams
Botpress - Open-source platform for developers to build high-quality digital assistants
Microsoft Bot Framework - Framework to build and connect intelligent bots.