Dialogflow - Conversational UX Platform. (ex API.ai)
Twilio - Brings voice and messaging to your web and mobile applications.
Octane AI - Octane AI offers tools to create a bot and engage customers and audience via messaging.
Swift SMS Gateway - SMS Gateway is your bridge between the Internet and the world of cell phone SMS text messaging.
Botpress - Open-source platform for developers to build high-quality digital assistants
Maytapi - Serverless Whatsapp Api with Chat and Agent support.