Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Geary - Geary is an email application built for GNOME 3.
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs