Mia for Gmail

Postbox is an email client that combines all of your email accounts into one program for use on your Mac or PC desktop. The software gives you access to both IMAP and POP email accounts, along with

Unibox is an application that aims to completely overhaul your email experience. Unibox resorts your email so that you can group the messages you receive by their sender. This unique feature

This is the software that Google should have developed itself.

Mailplane is the best way to use Gmail on your Mac. Use an unlimited number of accounts, get new mail notifications, use plug-ins and much much more.