There’s no debating that credit and debit cards are convenient, but typically the only places that you can use them are in businesses, or via the phone or internet. In 2009 the co-founder of Twitter, Jack Dorsey, set out to change that. He released a beta version of Square, a system that allowed mobile devices to receive card payments. A small card reader plugged into the device’s headphone port, and an app handled all the 1s and 0s. Two years later, Square is out of its debugging phase and available for general use.

The card reader is sent to users free of charge, and there are reportedly no activation, gateway, monthly, early termination or hidden fees, nor is a contract required to use the service. What there are are transaction fees – 2.75 percent + 15 cents for swiped transactions, and 3.5 percent + 15 cents for keyed-in transactions. These fees stay the same regardless of the amount of transaction, and are taken off as the transaction occurs, so no fee schedule is involved. The user pays nothing at all if they don’t use the service.

There is no limit on transaction amounts, and funds are automatically transferred into the user’s bank account after a 24-hour period. The system can also make refunds to buyers.

While Square accepts all major credit cards, the company does have a policy regarding what sort of products it will allow its service to be used to sell. The website states, “Our banks and the payment card networks have also determined that certain transactions, while legal, present high risk exposure to Square, our merchants and their customers,” adding that funds may be withheld from users caught violating that policy. The list of unacceptable transactions includes understandable things like illegal activity, drug paraphernalia and hate products, but also includes greyer areas such as raffles, adult entertainment and occult materials.

Square is compatible with iDevices and Android, but can currently only be used for purchases made within the United States.