Dialogflow - Conversational UX Platform. (ex API.ai)
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Octane AI - Octane AI offers tools to create a bot and engage customers and audience via messaging.
Botpress - Open-source platform for developers to build high-quality digital assistants
Botkit - Botkit is an open source developer tool for building chat bots, apps and custom integrations for major messaging platforms.
Expensive Chat - Chatroom where you pay per letter