Shift - Shift is the ultimate email client for managing Mail, Calendar, Drive, Slack, Asana, Jira, Evernote, and all your other favourite apps
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Mia for Gmail - A desktop email client for your Mac, without a browser !
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Mailplane - Mailplane is the best way to use Gmail on your Mac. Use an unlimited number of accounts, get new mail notifications, use plug-ins and much much more.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs