Currently in beta, BlinkMail aims to help you quickly and efficiently, get through your Inbox by using nothing more than arrow keys.
The small, free OS X app parks itself in your Mac's menu bar after installation. You will receive an alert for each new message in your Inbox.
Clicking on the app's icon lets you reply, star or flag, archive, or move a message to a folder using the arrow keys. Of course, you'll need to customize what each arrow key does to tailor the app to fit your needs.
As previously mentioned, the app is currently in beta, which means there are bound to be some issues when you use it. For example, I can only customize the action associated with the down arrow. But as with all betas, updates are sure to come along and fix any issues; just be sure to report them to the developer through the settings section of the app.
You will need to be running OS X 10.9 Mavericks in order to take part in the beta and give BlinkMail a try.
You can read more about BlinkMail, watch a fancy GIF demonstrating current and future features, and download it here.