Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Crisp Chat - Multi-channel customer support software
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
Heeduser - Heeduser is the customer engagement platform that helps companies build better relationships with their customers and prospects, through the better online customer community
csupport - cSupport offers Live Chat support. Ideal for small businesses and Entrepreneurs Worldwide.
Feedbackify - Feedbackify offers website feedback solutions that enable companies to engage with their customers.