Fetch Rewards works in a similar way to apps like Checkout 51 or Ibotta.
With Fetch, you scan a receipt from within the past 14 days, and it looks for certain products or brands.
If those brands were part of the receipt, then you receive a certain amount of points.

The ways that this app is awesome, however, is how FAST it is to earn enough points to get the rewards.
As a baseline, a $3 Amazon gift card (the lowest Amazon amount available) is worth 3000 points.
Each receipt that has an accepted item/brand on it gets 1000 points immediately, as well as the points for the item/brand.

Furthermore, there are some items and brands that are worth hundreds or even thousands of points, due to being labeled as "Special Offers".
All of this allows for the ability to earn rewards very quickly with minimal effort.
As for the brands themselves that can earn points, there are a LOT. Ranging from Pepsi products to Quaker to Kraft, there's a fair amount of variety available.
Finally, about the receipts themselves. I have yet to find any rules about the number of receipts you can enter at a time or from a date, so if you're one of those types that hoard receipts, this should be even better for you!

The app is available for both iOS and Android at their site: http://www.fetchrewards.com/fetchrewards
And while you don't have to, I recommend that you use my referral code, A6AWJ. It will get you AND me 1500 points with your first completed receipt.

I hope this app helps you guys out!