Google added the ability to run apps side by side in Android N but so far we could only run different applications side by side, which means if you wanted, say, two browser windows side by side, you'd have to install a separate browser alongside Chrome to do that.
Well, Android N Developer Preview 3 fixes exactly that. Now, you will be able to run Chrome windows alongside each other.
With a new option in the Chrome menu, you can move a tab to the space next to your current window, which then creates another instance, and then you can use it to open other tabs. The OS remembers your instances so even if you exit multi-window mode, it won't combine them together and you will get two instances of Chrome in the multitasking (or Overview) mode.
This is limited to Chrome for now but the OS doesn't limit multi-window to a single app, so other developers, say, Microsoft for Office apps, will be able to make their apps run multiple instances side by side.