OSX El Capitan split-screen (4-way)
On my El Capitan Mac, I use BetterSnapTool. It’s a very good program for managing multiple side-by-side windows. 

I even used it to to create a custom resizing command so my windows will not extend into the Notifications Area. 

Available on the Mac App Store. Also see the developer’s web site: https://www.folivora.ai/bettersnaptool