It's called Checkout 51.
Every week I get new "offers" on cash back for groceries. This week I get 50 cents cash back if I buy tomatoes, 25 cents cash back if I buy corn, 25 cents back if I buy onions, etc. etc.
They also advertise specific products (this week, cash back on Vlasic pickles, Dole pineapple juice, Doritos, etc. etc.)
After you "earn" 20$ cash back, they send you a check in the mail.
The reason I like it is that it doesn't matter where you buy the groceries/ how much you paid/ if you used other coupons. You just upload the receipt from wherever. I buy produce at Trader Joe's/ local ethnic stores that don't have coupons- and a lot of times it's "free" with the cash back! I mostly use this to accumulate money on produce and non-brand name items, since the app doesn't always specify brands (another example this week, is 25 cents cash back for "hot dog buns"- any variety).
You can find the app on your phone's play store.