Polymail - Native email app for email productivity.
Front - multi-channel inbox service for collaborative teams
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
Mailbird - Mailbird is the best email client for Windows 7, 8 and 10
Missive - Team communication app now supporting FB, Twitter & SMS