Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Drift - A messaging app that helps you grow your business.
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
Talkus - Chat with your website users from Slack
JivoChat - JivoChat is a live chat that enables you to talk to visitors on your website
HeyHi.sg - Video call with interactive whiteboard