Folks at XDA have ported the multi window app from Galaxy note 2 to Samsung Galaxy Grand Quattro phone. To get it on your phone, you must have a rooted phone and also should have CWM recovery installed on it.
For root, follow this post and to get CWM recovery on your grand quattro, read this post. After getting root + CWM, follow these steps.
1) Download this file and put it on your phone’s SD card. Now, reboot to cwm recovery (vol down + power)
2) Select, “install my zip from SD card” and select the file.
That is it. You have successfully downloaded and installed Multi Window on to your Galaxy Grand Quattro phone.