Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Smooch.io for Facebook Messenger - Message your customers from Slack, Front, a bot or anywhere!
SmoochBot - Open source on-boarding bot for conversational apps
GetChat.App - Add WhatsApp chat to your website for free
Hotline - In-app chat,real-time engagement & self-service for your app
Avochato - Text messaging for your business.