Apple
On Mac OS X El Capitan, you'll be able to split your screen in half with two different app windows with the new Split View feature.
It works by clicking the small green button on the top left of an app window, and you choose which half of your screen you want the window to occupy. You'll also be able to resize each window by clicking and dragging the point where both windows meet in the middle. In previous versions of OS X, users had to resize each window manually, which took much more effort and time.
While it's new for Mac OS X, it's a feature called Snap that's existed in the Windows operating system since Windows 7, and it's clearly a feature Apple couldn't ignore in its newest update of Mac OS X. To split your screen with two different apps in Windows, you need to click and drag the top of a window to whichever half of the screen your want it to occupy.
Screenshot