Botpress - Open-source platform for developers to build high-quality digital assistants
Dialogflow - Conversational UX Platform. (ex API.ai)
Octane AI - Octane AI offers tools to create a bot and engage customers and audience via messaging.
Chatfuel - Chatfuel is the best bot platform for creating an AI chatbot on Facebook.
Botkit - Botkit is an open source developer tool for building chat bots, apps and custom integrations for major messaging platforms.
Microsoft Bot Framework - Framework to build and connect intelligent bots.