Using NetPlenish, you go around your home and start scanning the bar codes on regular, everyday things you need or regularly buy: Diapers, soap, food, whatever. The app then goes out to a bunch of retailers and finds you the best price. Then, once you have your shopping list it will tell you the best deal it found on your entire list, plus shipping. But it's not done yet. That price is the most you'd have to pay once you agree to buy your list at at least that price. It then sends your entire list to the merchants and has them bid on it, potentially getting you an even better deal. Once your final, final, final price is determined and you pay, the app offers a guarantee that if you can find a better price for your entire list, it will send you a check for the difference. NetPlenish is a free app for iOS and Android devices.
Developers of the Decide app say they've created an algorithm that, based on things like price history and future product launches, will help predict for you the best possible time to buy an item so that you get it as the lowest possible cost. Each item has a graph that shows you where its price has been and where it's expected to go. And based on that graph you get a message that tells you to either buy now or wait. And that's based both on online prices and prices in stores near you. It also offers a guarantee called 'Got Your Back' if it tells you to buy and the prices of your item drops within two weeks. It too will cut you a check for the difference. Decide is also free and also for iOS and Android devices.