iPhone: You're not going to find a shortage of email apps out there for the iPhone, but Triage doesn't want to replace your email client. Its primary purpose is to help you organise your email when you're on the go.
Triage isn't meant to be a full-featured email client; it's all about organisation, and it works very well to that effect. Once you sign in with your Gmail, Yahoo, iCloud or any other IMAP email account, Triage gives you one screen with a stack of emails. Swipe up to archive the email or swipe down to keep it. You can compose brief replies, but that's not really the point; Triage is more about management.
While it would be nice if you could also sort emails into labels, the simplicity makes it handy when you're killing time productively on your phone.
Triage: Email First Aid ($1.99) [iTunes App Store]