Jack Dorsey, co-founder of Twitter, was in Boston this week recruiting MIT students to join him and his team at Square.

According to Boston.com, “the 400-person company based in San Francisco is looking to double in size over the next year, said Dorsey, as it prepares to expand into overseas markets and grow its customer base of 2 million merchants and small business owners that use its credit card readers for turning tablet computers or smartphones into mobile payment terminals.

What does Square do? The visual below should sum it up nicely for you, but in case you prefer words: Square gives retailers (and anyone, really) a simple way to process payments using mobile devices. This is particularly handy if you have a tech-savvy crowd – and who doesn’t have a smartphone these days?

Also, the Square reader is free and each transaction costs a flat 2.75% of the sale.

Boston.com also notes that “fifty percent of smartphone owners say they are interested in using their devices to make payments, according to a recent Forrester report on mobile payments. And younger users express more willingness to pay with their phones.

Dorsey said traditional financial companies such as Citi Ventures and Visa Inc., another Square investor, are funding the company because they want to fuel innovation in a sector that has been slow to adopt technological change. What is more, he said, Square is giving many small-business operators, such as artists or hairdressers, who previously would not be able to afford costly credit card systems, the ability to start accepting plastic.

So would YOU relocate to San Francisco to work for Square?