Appzapp is app news website where they show best apps that are on sale or have gone free. Eventually, I found that they've got a channel on IFTTT(If This Than That). [For all those who don't know about IFTTT you should head over to their site. Their homepage content can easily make you understand the concept behind the app. It was also listed as top app in April 2014.]
Well, on Appzapp's channel they've created many recipes. Recipes include new apps on sale and those that have gone free. You can have a notification for that through pushbullet or a direct android notification for instant response. Also you can get an email digest everyday at specific chosen time. And of course you can create a recipe of your own. Same goes for apple app store. So, go activate them if you really get excited when your favorite paid app goes Free.(who doesn't!)
For all those who have never used IFTTT, we've gotta walk through below.