If you've ever heard of Merlin Mann's Inbox Zero concept, then you know you can boost productivity by focusing only on the emails that matter. Mailbox ($Free) is designed to do exactly that. It features a simple, gesture-powered interface that quickly lets you archive or delete mail, or "snooze" it until later so you focus on more important messages — they'll return to your inbox later. In addition, it organizes conversations into a chat-like structure, making it more easy to follow long threads. It's available now for the iPhone and works with all Gmail accounts, but you'd best be prepared to wait a while before you get to use it — last time we heard there was quite a line.