Nylas Mail - The Nylas Cloud API powers your application with email, calendar & contacts features. Built-in features for better email, calendar, and contact management.

Polymail - Native email app for email productivity.

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

Canary Mail - Privacy-aware email app for Mac & iOS

Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.

Flow-e - Turn your Gmail or Office365 inbox to a Visual Task Board.