IBM Watson Assistant - Watson Assistant is an AI assistant for business.
Dialogflow - Conversational UX Platform. (ex API.ai)
Botpress - Open-source platform for developers to build high-quality digital assistants
rasa NLU - A set of high level APIs for building your own language parser
Tars - TARS enables users to create chatbots that replaces regular old webforms.
Hubot - Hubot is a standardized way to share scripts between everyone's robots.