Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Chatlio - When you have a business to run, your average instant messaging software just will not do. You need an internal presence upon which your entire team can collaborate on. Read more about Chatlio.
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
Re:plain - The simplest live chat in the world
JivoChat - JivoChat is a live chat that enables you to talk to visitors on your website
ChatSupport.co - ChatSupport is a live chat software for websites which lets you interact with website visitors and customers through customizable chat widgets.