Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
WikiPro - All-in-one Business to Customer Communication
Pure Chat - Pure Chat provides FREE live website support and sales chat without the hassle! It's web site chat, simplified.
Heymarket - The professional way to text message. Your customers are mobile. Heymarket helps you manage those relationships from your smartphone.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Respond Flow - The Mailchimp of SMS