SoftWap

First you need to Upgrade Android One to Marshmallow  Now install any Custom Recovery Now Flash the Zip file " MultiWindow " Restart your phone Go to Settings --> Developer options   "Turn On" Multi-Window Mode Enjoy MultiWindow        Video Guide :-                          

Here are some of best recoveries for Android One, which you can flash through Rashr Flash Tool Philz Touch                 Download Here TWRP      Download Here CWM     Download Here