Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Intercom Facebook integration - Read, manage & respond to Facebook messages from Intercom
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
Crypton.sh - SMS - Secure Anonymous SMS in the cloud (and a phone number)
JivoChat - JivoChat is a live chat that enables you to talk to visitors on your website
Live Chat by Sumo.com - Instantly communicate with customers, prospects & visitors