Square made its debut at the end of 2009 as an easy way to let people quickly accept physical credit card payments from their mobile phone. According to TechCrunch, the application has been in limited beta since then and their website claims that a flower cart in San Francisco is using Square to take payments from customers. Also using the service is a glass factory in St. Louis, a jeans store in NYC plus a coffee bar in SF. There are no contracts, monthly fees or hidden costs with Square. To use the device you just swipe the credit card from any device with an audio input jack - and as a payer, your receipt gets sent to your email or mobile phone instantly. (Another feature...you can use a text message to authorize every payment in real-time).
Two campaigns have picked up on the idea and are now using it for political fundraising. Silicon Valley VC, Josh Becker, who is running for state assembly in California's 21 district, has been using Square at fundraising events - and a congressional candidate running in New York's 14th district uses it also.
Here is a video of how Square works in action.