Platform: Android, iOS
I'm all about getting free stuff. After all, what's better than free? One tool I use in the pursuit of being cheap is Bing Search. Microsoft offers an incentive to those that use Bing to search the web in the form of credits per search. Earn enough credits and you can redeem them for things like gift cards or entries into sweepstakes.
Users can earn up to 28 points a day for performing searches on their PC, mobile device, and for completing special searches (usually three a day). Over time, it adds up and one will have enough to get the gift certificate of choice. Myself, I invest in the Microsoft points cards which fuels buying things like loot boxes in Overwatch. It only takes a few minutes a day to complete the searches and within a couple of weeks, you'll have enough for another $5 gift card.
Having the app makes it easy to keep track of what you're doing per day and ties directly to your Microsoft account. Note that using the Bing search engine without signing in won't reward the points to your account.
Other than that, the app provides the same search functionality as Bing on PC. I won't try and persuade you to use it. I took the Pepsi Challenge and made the switch. It works for me, but I can understand if it doesn't work for others. There are too many good search engines out there to be tied down to one.
So if you're looking for an easy way to get some free stuff, Bing Search is yet another way to do it.