Android: If you like to look at your email as if it were a to-do list, then Blue Mail is designed with you in mind. It lets you snooze mails for later so they act as reminders, and you can even turn your inbox into a task list and mark each message as "done".
It's generally a good idea to separate your email from your to-do list, but that's not for everyone. The recently launched Mailbox for Android does a good job of turning your email into a productivity zone, but it's limited -- you need a Dropbox account, you can't save attachments to your local memory, and it works only with Gmail and iCloud.
Blue Mail supports a vast range of email providers, including Gmail, Yahoo, Outlook, iCloud, AOL and other POP3 accounts. It has threaded conversations and a profile picture, which will be familiar to users of Gmail for Android.
Swipe left on any message and you'll get two options: Done and Delete. The latter is self-explanatory, while the former puts a checkmark on the mail, so you know that you have addressed whatever needs to be addressed. If you get a lot of work mail, this can be an invaluable addition.
Swipe right on any message and you get two shortcuts to set a reminder for that mail. Both are named "Later" so it gets confusing at first, but the first is a shortcut to snooze for three hours while the other lets you choose when you want to get the reminder. The shortcut's duration can be changed in the app's Settings.
Settings also let you choose whether you want your default filter to be all the mails in your inbox, or only those which haven't been set to "Later" or marked as "Done". To check all of these task-listed emails, there's a separate Tasks view you can turn to.
Blue Mail is a simple and efficient app that gets things done in your inbox, so give it a whirl.