GrexIt - Manage Tasks, Customer Support and Sales right from your Gmail inbox. Turn your Gmail into a powerful collaboration tool.
Polymail - Native email app for email productivity.
Mailor - Shared inbox, team portal and smart notifications
New Gmail - The new version of Gmail web
Airmail for iOS - One of the best Mac email clients, now on iPhone
Mailbird - Mailbird is the best email client for Windows 7, 8 and 10