Chatfuel - Chatfuel is the best bot platform for creating an AI chatbot on Facebook.
Dialogflow - Conversational UX Platform. (ex API.ai)
BotStar - BotStar | Engage Customers Online with Live Chat & Chatbots
Octane AI - Octane AI offers tools to create a bot and engage customers and audience via messaging.
Telegram bot API - The Bot API allows you to easily create programs that use Telegram messages for an interface.
Botpress - Open-source platform for developers to build high-quality digital assistants