Samsung Galaxy Note II has a feature called Multi Window that allows two apps to be displayed on the screen at the same time, improving your productivity.
This feature only supports some applications, but now thanks to community all these restriction were removed. You can now add any application to the list of those which can benefit from multi-window with the help of a mod.
Installation is rather simple and you only need to flash it in Recovery mode. You need to find the proper mod compatible with your version of the ROM and you will also have to check out whether it is odexed or deodexed.