Thanks to kind folks at XDA, the Samsung galaxy core users can have multi window functionality on their phones. All you have to do is get the multiwindow.apk file from here; put it on the root folder of your phone; reboot to cwm recovery; install my zip from SD card and install it on your phone.
To use multi window on the phone, there is need to have root access, as well as CWM recovery, and can be used on any deodexed Galaxy Core ROM.