NEW YORK ( MainStreet) -- With less than two weeks to go before Christmas, shoppers can use all the help they can get, and one of the most useful tools can be a store's mobile shopping app. Unlike more general mobile shopping apps, retailers' own apps are geared directly toward helping customers find what they need as fast as possible and find out about deals while inside their store.

Mobile shopping has taken off this year. As of December 8, 20% of all online shopping has taken place via a smartphone or tablet, and on certain days even more people opt to buy while on the go. According to Comscore, mobile buying accounted for $361 million of spending on Thanksgiving, 26% of the total spent online. It accounted for $436 million on Black Friday (22% of the online total), and $548 million on Cyber Monday (21% of the total).

Here is a list of what the top retailers offer via their apps:

Wal-Mart's in-store app is designed to save its customers time and money. Savings Catcher goes online to see whether a local competitor has a better price on an item you just purchased at Walmart. If so, the store gives the shopper the difference between the two on an e-gift card. The app also helps create a shopping list by allowing you to scan an item's barcode, type in its name or render it via voice recognition. Then to save you a trip to the store, the pricing and availability feature will check if the nearest has the item in stock. If it's not available, you can just hit the shop button and buy it online.

Target's app contains the usual shopping list builder and store locator but also has two features perfect for holiday shopping. These are Cartwheel and Wish List. Cartwheel is one part coupon collector and one part game. Customers shop and scan in offers, and the app checks to see if there is a Cartwheel discount, which can range from 5% to 50% off. If a discount exists, it is added it to the list and at checkout the app generates a barcode that is scanned by the cashier and the savings is displayed. Up to ten items can be saved on your Cartwheel list for your next visit, but additional slots can be earned by getting badges. The Wish List feature allows parents to track and share the items their kids want.

Best Buy's app is a bit more straightforward, simply offering all of the chain's normal Website offerings in a mobile format. A couple of twists on the app, though, include a social media feature that gives a customer My Best Buy bonus points for checking in at a store, and the app will also display daily deals, in-store clearance and open-box items available in stores.

Amazon gives shoppers the opportunity, which retailers loathe, to see a product in a store but then hop online and see if it can be purchased for less. Just capture the product's bar code, and the app does a quick price comparison; if a better deal is found, it can be bought right from your phone.

Macy's focuses on making your shopping experience as painless as possible. It gives access to Macy's entire inventory. If you're having a hard time making a decision, a simple bar code scan will link to a review and videos on the product. Shoppers also have access to in-store deals through the app, and if you are in a giving mood, you can pay your store credit card balance right from your device.

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Kohl's app gives quick access to some of the chain's shopping programs. The app keeps track of the shopper's Kohl's Cash, which gives you cash back on purchases. The cash is stored in the Kohl's Wallet along with all of the other store's special offers. The customer can download these from Kohl's or use the phone's bar code scanner to add in offers sent via snail mail.

Costco's app, just like its warehouse stores, is a bit bare-boned but filled with things to buy. Customers can create shopping lists and get the store's weekly deals, and if they don't see what they want in the store, they can buy it online directly using the app. One useful tool for the holidays is the photo feature, which allows the user to directly upload images to the store's photo center for prints and cards.

Sears doesn't want to lose customers because they can't find talk to a sales associate. With its Members Assist feature, found on its ShopYourWay app, a person can connect directly and chat with an in-store Sears staffer. The app also has a social media function so shoppers can let their friends know where they are and in return get Sears reward points.

--Written by Doug Olenick for MainStreet