Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Twilio Flex - The programmable contact center platform 📱
MessageBird API on StdLib - Purchase numbers, send SMS and more with one line of code
Drift - A messaging app that helps you grow your business.
LoopMessage - LoopMessage is a perfect macOS tool for personalized mass messaging via iMessage/SMS, WhatsApp, Facebook Messenger, Telegram, Viber, and Skype.
Twilio - Brings voice and messaging to your web and mobile applications.