Android N has a new feature - Multi Window Mode. It enables two applications to be active side-by-side (actually one one is active, other one is paused but we can see both s
I don't think that an api for the thing you want to do exists, You could try making your app have two fragments on each side of the screen. With a black bar in the middle, make each fragment resize according to the "X" position of the bar. :)