Dialogflow - Conversational UX Platform. (ex API.ai)
Microsoft Bot Framework - Framework to build and connect intelligent bots.
Botpress - Open-source platform for developers to build high-quality digital assistants
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
Messenger Platform - Discovery, chat extensions, and richer experiences
Hubot - Hubot is a standardized way to share scripts between everyone's robots.