Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Pure Chat - Pure Chat provides FREE live website support and sales chat without the hassle! It's web site chat, simplified.
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.
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
HeyHi.sg - Video call with interactive whiteboard