[See the Secret to Living Well on $20,000 a Year.]
8. Square (Free: iPhone, iPad, Android). As we move toward a cashless society, the need for people to be able to accept credit cards has spurred a growing niche. Does a friend owe you $40 but can never pay because he "forgets" to carry cash? Are you running a garage sale? This groundbreaking free app, with its no-charge plug-in hardware, turns your device into a credit card machine, thanks to the quarter-size square reader that you attach. (Sign up at squareup.com, and the company mails you one.) You'll be charged a flat fee of 2.75 percent for swiped transactions. If you enter card numbers manually, your costs rise to 3.5 percent of the takings plus 15 cents per transaction because of the higher risk of fraud.
9. Loan Shark (Free: iPhone, iPad). Many consumers get tripped up by failing to realize the true costs of a loan. This handy app allows to you pop in any three pieces of information (e.g., loan amount or interest rate), and Loan Shark fills in the missing ones so you know exactly how much in the red you'll be. You'll also be able to access amortization schedules, and the results can be saved as favorites to review later in side-by-side comparisons. One useful feature: You can see the effect of extra (or larger) payments.
[See 6 Steps to Dig Out of Debt.]
10. ReceiptLoader (App is free; monthly plans start at $7; iPhone, iPad). If you travel or have a lot of work expenses, this app is more than worth the subscription fee. It can save you valuable time and ensure you don't forget expenses or lose receipts. Use your phone to snap a picture of your receipt, and the app identifies key information and categorizes it. When you have to submit backup for your expense report, you can export the data into one of several file types or email it from your phone. Choose from three plans: $7 buys you 30 receipts recognized monthly, $23 (100 receipts), and $42 (500). If you only have the occasional work expense, try Mobile Receipt, a similar app that's free for up to five receipts per month. It doesn't have the automatic data recognition, though.
11. Your bank's mobile app (Free: iPhone, iPad, Android). Most of the nation's 16 largest banks now have at least one mobile application, notes a recent study by financial services research firm Corporate Insight, and the number of financial institutions catering to mobile customers is growing rapidly. Besides letting you pay bills from your phone, some apps have particularly impressive features: Chase, Charles Schwab, and USAA, for example, allow you to deposit checks by snapping a photo of the front and back.
12. CalcMoolator Pro (Free: iPhone, iPad, Android). This app is a one-stop math shop, with just under 200 financial calculators that can help you figure out your hourly wage from your salary, say, or compare renting versus buying a particular home. You can also road-test debt reduction scenarios based on the factors that matter most to you—for example, whether to pay off a credit card debt in a year or at a fixed low amount for as long as it takes.
Corrected on 12/28/11: An earlier version of this story incorrectly stated that Mint offers an app that runs on the Symbian system.