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
Front - multi-channel inbox service for collaborative teams
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
DuoCircle - DuoCircle provides enterprise spam filtering and email management solutions.
Missive - Team communication app now supporting FB, Twitter & SMS
Nylas Mail - The Nylas Cloud API powers your application with email, calendar & contacts features. Built-in features for better email, calendar, and contact management.