Mailbox is great mobile client for Gmail (Boomerang for Android is pretty slick too). Mailbox was acquired by Dropbox a little over a year ago and yesterday they announced they were releasing some additional functionality, namely an Android version of the app.
Mailbox is also available on the iPhone and iPad. You can sign up for a beta version for OS X but we haven't gotten our hands on it yet.
While our go to mobile client is Gmail, Mailbox works great with your business or personal Google Accounts and offers some pretty cool features. The objective of Mailbox is Zero Inbox, the ability to reach a point where email is "done", if there is such a place anyway. In our testing Mailbox works great.
Noteable features are:
The ability to quickly long or short swipe to Delete or Archive messages, not too different from Gmail although the swipe action in Mailbox can do either, while Gmail makes you select one or the other which can be toggled in Settings.
Mailbox provides the ability to quickly set reminders for emails you can't address immediately or need to address at another particular time. We can leverage services like Right Inbox and Streak to achieve this on our laptop but this was more difficult on mobile. This is a great feature.
We also like the ability to easily create lists right from your Inbox. You can create Lists specific to your workflows, processes, projects, etc. and quickly add emails to the appropriate List. You can think of Lists as similar to how you may use Labels to organize and tag messages.
That brings up another important point, Mailbox does not allow you to use your Labels or support Gmail's Categories. If you're a heavy Label User or depend on Categories, Mailbox is not for you. It isn't an 'all or nothing' proposition though, you can have both Gmail and Mailbox on your mobile device.
Mailbox also provides a "unified Inbox" which many people prefer. It's very easy to add your Google Account. Simply go to "Add Account" in the Mailbox Setting and Select Google. You're all set. If you check out Mailbox, let us know what you think.