Multiwindow Plus enables a HIDDEN feature in your device that adds more functionality to the multiwindow sidebar. At the moment, Samsung multiwindow feature only allows dual view. This app or mod so to speak adds floating, docking and quad view features on the multiwindow tray.
This app only enables the hidden feature and has nothing to do with how the said features work. There may be graphical issues or stability issues and that is why Samsung has disabled them in the production version. It also does not guarantee that it will work on your device or ROM due to various reasons. And if it works at the current firmware version, there is no guarantee that it will work on future firmware updates. Please TAKE NOTE of these issues before you proceed.
You need to Root you Samsung Galaxy Note 3 to use this app. If you don't know what is rooting, read this Article.
Download Free version of Multiwindow Plus from here and if you like the developer's work consider to buy the donate version from Google Play.