The Android N developer preview seems to be bringing in a whole bunch of new changes to the system, with many of them making some excellent improvements that are sure to have users chomping at the bit to get their hands on the new version of software. One of those changes that users will be hard pressed to miss is the larger cards for the open apps on the recents screen which users can get to by tapping the overview button, which happens to be the little square button on the right-most part of the navigation bar down at the bottom of the display. Google also finally added multi-window with the Android N developer preview so users will be able to open up two apps at once and have them both displayed on screen simultaneously.
In addition to the larger cards in the recents menu, Google has basically powered up the overview button to do a whole lot more than just take you to the screen where you can see your currently open apps. Instead of just tapping on the overview button to open up the recents menu, if you're on the homescreen and you double tap it, you can immediately open up the application that you used last. That alone would be a nice new addition even if it was the only change, but it isn't.
Alongside the larger cards and last app access, users can apply the same double tap to the overview button from within an app and it will take them to the app they had used prior to the one that they were in before the one they have currently on screen. With the recents menu open, continuously tapping the overview button will let you cycle through the open apps cards until you settle on the one you wanted to use, at that point you can simply stop tapping the overview button and the app you're on will open full screen. There are also a couple of long-press options baked into the overview button now too, as you can long-press on it to switch to split-screen mode, but if you swipe your finger over an app after long-pressing you can see a preview of that app without actually opening it. Just this small handful of changes to the overview button really seems to make a difference for power-users, and while Google may not end up keeping all of these functions, they can just as well add in more before the final build is pushed out to the public.