Dialogflow - Conversational UX Platform. (ex API.ai)
VISEO Bot Maker - Create chatbots and vocal apps in just a few clicks
Octane AI - Octane AI offers tools to create a bot and engage customers and audience via messaging.
boteria - Business chatbot has never been so simple and fast
Botkit - Botkit is an open source developer tool for building chat bots, apps and custom integrations for major messaging platforms.
Botpress - Open-source platform for developers to build high-quality digital assistants