This can be done through the use an app called PGAF. The idea behind this app is very simple. It allows you to see which particular paid android application on Google play store can be download free within a particular period time. Most application development companies generally do promotions frequently for promoting their products. This app just crawls through this apps on play store and see if there are any apps are gone free for the day and lists out this apps.
Download Link:- https://play.google.com/store/apps/details?id=com.chikisoftworks.pagf&hl=en
Here is another apps like PAGF which allows you to get paid apps for free.
You can download the app from google play.
Link:- https://play.google.com/store/apps/details?id=net.tsapps.appsales&hl=en
This app also works similar to PAGF, shows a list of apps categorized that are free for a limited time. Sometimes you can find interesting apps like Games and Themes available for free.
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