Message.io - Make your chat bots cross-platform
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.
impossible.bot - Get a chatbot without writing code or any special content
Botkit - Botkit is an open source developer tool for building chat bots, apps and custom integrations for major messaging platforms.