Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.

LiveChat - LiveChat - premium live chat software. Approach customers directly on the website, make connections and drive more sales using LiveChat.

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

Olark - Real-time chat and monitoring of your website visitors through Google Talk and Jabber.

JivoChat - JivoChat is a live chat that enables you to talk to visitors on your website

Zendesk - Zendesk is a beautiful, lightweight help-desk solution.