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.
Landbot - An intuitive no-code conversational apps builder that combines the benefits of conversational interface with rich UI elements.
Botkit - Botkit is an open source developer tool for building chat bots, apps and custom integrations for major messaging platforms.
Botsify - Ever wonder if you could replace your live chat support system with a chatbot?. Its possible now with Botsify Chatbot For Website.