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
JivoChat - JivoChat is a live chat that enables you to talk to visitors on your website
Heymarket - The professional way to text message. Your customers are mobile. Heymarket helps you manage those relationships from your smartphone.
tawk.to - tawk.to is a free live chat app that lets you monitor and chat with visitors on your website or from a free customizable page
Respond Flow - The Mailchimp of SMS