I love Square.
Square is a company out of San Francisco, CA that helps the average Jane or Joe to process credit card payments. In other words, everyone can now accept credit cards on their mobile device without having to sign up for a credit-card terminal, which often requires a contract for a certain amount of time and a monthly fee.
For the psychotherapist that can’t afford a credit card terminal or doesn’t want to sign a contract to have one, this is an optimal device. For the social worker who has worked hard to publish a book or develop a series of tools, this can also be beneficial to you to sell your work.