1. True multiwindow multitasking
If you open the overview screen and perform a long press on an app title, you can now drag that activity to a highlighted portion of the screen to put the app in a multi-window mode. Long-press the overview button, and the device will put the current app in multi-window mode itself, then open the overview screen to let the user choose another activity to share the screen with. You can also now drag and drop info from one window to another while they are sharing the screen.
In Android N, the system fills the screen with two apps, showing them either side-by-side or one-above-the-other, depending on if you are in portrait or landscape mode. The user can drag the dividing line separating the two to make one app larger and the other smaller. On Android TVs or the Nexus Player running Android N, apps can put themselves in picture-in-picture mode, allowing them to continue showing content while the user browses or interacts with other apps.
On larger devices, like tablets, makers can now choose to enable freeform mode, in which the user can freely resize each activity. If the manufacturer enables this feature, the device offers freeform mode in addition to split-screen mode.
2. Bundled notifications
Instead of showing notifications chronologically, Android N now bundles notifications from the same app together - for example threads from a messaging app. Those grouped notifications can be expanded for preview by using the two-finger swipe, or by tapping the new expansion button - this way you can read a whole email message directly from the notification shade, for instance.
3. Direct reply notifications
Building on the notification improvements, Android N now allows you to reply to incoming message notifications directly from the status bar, without ever leaving the notification shade where you can also preview the whole message or email. Just drag it down with two fingers to expand and scroll the text, then hit the quick reply button to shoot a sassy comeback.
4. App switch with the overview button
With N, you can switch between active apps without even touching the screen, by simply double-tapping the overview button on your phone, which allows you an extremely easy way to go back and forth your two most recent apps, for example - nothing unseen, but very useful nonetheless.
5. More Quick Settings options
When you pull down the notification bar now you get one short set of quick toggles, or you can expand for the full monty, which now includes many new toggles, like an auto-rotate, clock, battery and other new shortcuts, plus an edit and rearrange option - you know, just like on most Android overlays worth their salt.
6. The Nightman cometh
Not necessarily a new feature, as it was present in Marshmallow before the public version did hit, but Night Mode is now an integral part of Android N, throwing a darker or warm-hued background over the interface so you don't get your retinas burned at night with bright white backgrounds.
7. Data saver
Again something that can be seen in manufacturer overlays, the new Data Saver option " helps reduce cellular data use by apps, whether roaming, near the end of the billing cycle, or on a small prepaid data pack. The system blocks background data usage and signals apps to use less data in the foreground wherever possible — such as by limiting bit rate for streaming, reducing image quality, deferring optimistic precaching, and so on." If you want some apps, like your Facebook Messenger, to always be connected, you can set an exception for them in the Data Saver menu, which is neat.
8. Improved file browser
While the integrated file browser is still hidden under the Storage>Explore menu, it now gives you more file options than simply copying, and has a handy side menu for faster navigation.
9. Display calibration
Just like on many manufacturer overlays, Android N will now let you calibrate the screens colors, though instead of more humanly understandable profiles like "warm", "cold," "Movie" or "Photo" modes, it opted to simply give you RGB sliders in the System UI tuner menu.
10. Extra power efficiency
In Android N, the Doze mode we know from Marshmallow additionally saves battery whenever the screen turns off by cutting off all background processes. Fret not, though, as most important apps are optimized for Doze, so you won't miss an alarm or when someone writes to you on WhatsApp - it's just that the phone won't be constantly on its toes to wait for those to appear.
With Android N, Google continues to invest in Project Svelte, an effort to reduce the memory needs of Android so that it can run on a much broader range of devices, by making background work more efficient. It has made the JobScheduler dev tool more capable, for instance, so now it can be used to react to things like changes to content providers.
11. Improved Java 8 language support
This is under-the-hood improvement you won't see, but Android N brings Java 8 language to the platform. Android's Jack compiler now helps reduce boilerplate code, lowering the footprint and development time. Of course, some of the new Java 8 language features will only be available on Android N and above.
12. Screen Zoom
Android N enables users to set the display size, which magnifies or shrinks all elements on the screen, thereby improving device accessibility for users with low vision. Users cannot zoom the screen past a minimum screen width of about 320dp, though, which is the width of a smallish phone like the Nexus 4, for instance.