If you are rooted and on the last KK ROM it's possible to have 3 or 4 apps opened at the same time on the same screen, read further...
Make a backup, just in case.
Open your /system/etc/permissions folder,
add .bak at the end of com.sec.feature.multiwindow.xml,
download the attached zip (DO NOT FLASH IT),
copy the files to your /system/etc/permissions folder,
set their perms to rw, r, r or 644,
Open any app from the flash bar (the multi windows app launcher on the side) and open a second one.
Now open a third one and drag it to any side, it will take one quarter of the screen. Open a fourth app, same story, now you have 4 apps opened on the same screen.
Every app is fully resizable, both in lenght and in width...
I'm sorry, I can't take any screenshot from my phone, but if you want to see how it looks do a google images search with "quad view multi window".
Enjoy and stay tuned, there's probably more to come!!!
Credits: @xperiacle @THEDEVIOUS1