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