With the first developer preview release of Android N now a few weeks behind us, we're still finding plenty of new changes in the new version of Android. This change here isn't actually one that is meant for primetime, considering you do need to do some tinkering with command line to get the freeform window mode working on the Android N Developer Preview. Essentially what this is, is a way for you to have all kinds of windows open. And instead of the window using up the entire display, you can have it use up a tiny bit of the display. Think Windows or Mac OS X. It can be very helpful, especially for those that may use their Android tablet as their main computer.
Now we have no clue whether this will be in the final version of Android N come later this summer. But it does appear that it's something that the Android team is working on in Mountain View. One of the big new features in Android N is the multi-window mode, which this appears to stem off of that feature. Multi-window we saw in Android M last year, but it disappeared before the final release in October.
As far as how to enable the freeform window mode in Android N, it should be noted that if aren't sure how to use ADB and Fastboot commands, then you should probably stay away from trying this. Having said that, you will also need your bootloader unlocked and the Android SDK tools installed. So you'll want to flash a build of the TWRP recovery to your device. After you have flashed the custom recovery, you will need to mount the system partition as being writable. This way your computer can write to the partition. On your computer, you'll need to open up command line or ADB Shell and enter the following commands:
sed -e "s/live_wallpaper/freeform_window_management/" android.software.live_wallpaper.xml >freeform.xml
That's all you need to do. Once you've done that and rebooted your device, you should have freeform windows on your Nexus or Pixel C device. It's pretty simple, but not worth the trouble of having extra bugs if you are using this as your daily driver device.