Here are features of the Android N Developer Preview that have been kept quiet13
Just when you thought that you had the Android N Developer Preview all figured out, Lifehacker has discovered some features on Android's next build that up to now have been kept quiet. Right off the bat, let's get started with the new double tapping feature. Tap the Recents button twice and you will be returned to the last app that you had open on your phone. And if you want to return to a different app, keep tapping on the Recents button until the app you want appears on the screen.
Next, the file manager introduced in Android 6.0, which had limited capabilities, does more than just copy files and allow you to browse folders. Called Explorer, you can move files and rename folders and create folders with Android N. You will be able to uninstall the third party file manager app you've been using. And with Android N, once you block a phone number it will stay blocked even if you reset your phone or buy a new one. Voicemails coming from that number will be deleted.
With Android N, you will be able to set Do Not Disturb to be disabled automatically when a set alarm goes off. That seems easy enough to understand, even for the Android DND feature which usually has written directions as clear the Hudson River. And for those Android users jealous of the Night Shift feature coming to iOS 9.3, Android N will bring Night Mode. This darkens the screen from the usual black-text-on-a-white-background look. Users will be able to set Night Mode to go off at certain times and locations. Users will also be able to set the color temperature. Night Mode was a feature found in the Android M Developer Preview, but was pulled before the build became final. With Apple offering Night Shift, Android N's Night Mode might survive this time.
With Android N, apps will install faster, and whenever there is an update to the OS, you won't have to wait for all of your apps to optimize. And lastly, emergency contact numbers can be kept on your home screen along with other information like your full name, address, date of birth, blood type, known allergies, medications, medical conditions, organ donor status, and emergency contacts. The only problem is that anyone with your phone can have access to the information if they open the emergency dialer.
source: Lifehacker via BGR, AndroidPolice