Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Avochato - Text messaging for your business.
Pure Chat - Pure Chat provides FREE live website support and sales chat without the hassle! It's web site chat, simplified.
Postscript - Like Mailchimp for SMS
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
GetChat.App - Add WhatsApp chat to your website for free