Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs
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
3CX - Hosted PBX with CRM integration and mobile apps
JivoChat - JivoChat is a live chat that enables you to talk to visitors on your website