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