Mailspring - Mailspring is a mail client for Mac, Windows and Linux.

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

Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!

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

The Bat - The Bat! is a secure desktop email client for Windows, designed to protect your correspondence against third-parties and to save your time.

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