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

Email Architect - All-in-one system to write, manage and organize email

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

KanbanMail - A Kanban board for your emails.

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

DuoCircle - DuoCircle provides enterprise spam filtering and email management solutions.