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.
Tars - TARS enables users to create chatbots that replaces regular old webforms.
Botpress - Open-source platform for developers to build high-quality digital assistants
IBM Watson Assistant - Watson Assistant is an AI assistant for business.