Polymail - Native email app for email productivity.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
HEY - Email at its best, new from Basecamp.
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Canary Mail - Privacy-aware email app for Mac & iOS
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs