My wife sells pottery at weekend craft shows. Taking credit cards used to be a big problem because wireless scanners are expensive. Then we found Square. You download the software, and they send you (for free) a little plastic square that plugs into the headphone jack of your smartphone. You can then process charges for VISA, MasterCard, Discover and American Express cards. The processing costs less than competing services; there's no monthly minimum and no per-swipe charge. The percentage you pay from each transaction is also competitive. The program is easy to use: just enter the amount and swipe, then the customer "signs" the touchscreen. You can send a receipt to the customer by e-mail showing the date, time and location of the purchase -- you can even include a photo of the product. And your money will be in your bank account the next day. Easier and less expensive than the alternatives, Square is a revolutionary combination of an app and a service. -- Alfred Poor

Square

OS reviewed: Android

Other OSes it works with: iOS

Price: Free app; 2.75% for swiped transactions; 3.5% plus $0.15 for keyed-in transactions