Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Zopim - Live chat is a faster and more personal way for you to engage your customers. Free for 14 days. No credit card required.
Crisp Chat - Multi-channel customer support software
Mutiny - Personalize your website for each visitor
Chatra - Live chat software that helps to increase revenue and collect feedback providing an easy way for website owners to talk to visitors in real time.
ChatinBox - A conversational user engagement platform for your users