One of the headlining features in Android N, announced earlier today, is Multi-Window. Something that many users have been asking for from Google for years. We actually saw it appear in the developer previews for Android M last year. But it appears that it wasn't completely ready for primetime. Now it's here in Android N and ready to roll! It's a pretty simple feature and it is also compatible with all Android apps, definitely a nice thing to have.
To get started, you'll need to enable developer options and at the bottom of the developer options list, there is an option to "Force Activities to be Resized". Now you'll be able to use multi-window as Google intended. Just long-press the recents key and you'll be in multi-window. However, it doesn't work on the home screen. This only works when you are in an app. Both apps that are being used in multi-window are also active at the same time, so you are able to use them both simultaneously. You are also able to resize these windows within multi-window.
If you want to get out of multi-window, simple long-press recents again, or you can grab the divider and toss it away. Swiping down will leave you with the top app open and swiping up will leave you with the bottom app open. There's no way to swap apps just yet, however that will likely be coming down the line. Remember that this is just the first developer preview. So things are bound to be a bit buggy. But it will get better as we get more developer previews. It isn't super buggy, at least in our short time playing around with it. Which is always nice.
Multi-window does work with all Android apps, as mentioned already, and will be a part of Android N. What will be interesting is if we see this multi-window appear on skinned devices like HTC, LG, Sony, Samsung and others when they update to Android N eventually. Currently, Android N is slated to be rolling out to everyone in Q3, so around August or September of this year.