Square is a a platform for iPhones, iPad (they already have a gorgeous app) and Android phones and laptops (in the future) that with a free credit card reader plugged into the headphones jack will allow to accept payments with credit cards. It is super nice app.
I don’t have a business but if I would, I wouldn’t buy a register machine, just an iPad. It will even create a community allowing to see the photos of who buys, etc…
Take a look at their website it is better to understand what it is about.
In February 2009, Jim McKelvey wasn’t able to sell a piece of his glass art because he couldn’t accept a credit card as payment. Even though a majority of payments has moved to plastic cards, accepting payments from cards is still difficult, requiring long applications, expensive hardware, and an overly complex experience. Square was born a few days later right next to the old San Francisco US Mint.
Today the Square team is focused on bringing immediacy, transparency, and approachability to the world of payments: an inherently social interaction each of us participates in daily. We’re starting with a limited beta and rolling out to everyone in early 2010.