Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Polymail - Native email app for email productivity.
MailClark - The Slack bot for external communications
Morning Mail - A new way to manage your mail. Tinder for email.
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.