Google Opinion Rewards 

Price: Free

Google Opinion Rewards is easily one of the best free Android apps in the Google Play Store. To use this app, you simply download and install it, then open it one time. After that, the app will periodically notify you to ask you some questions about where you go, what you do, and what Google products you use. You’ll get credit for use in the Google Play Store every time you answer a survey. That credit can go toward buying yourself apps or games on Google Play.

It’s a great way to expand your collection without spending real money. At worst, everyone should have this app installed. It is only available in some regions, so our international readers may be unable to use it.