This thing plugs into your phone, and charges credit cards. What a world we live in.

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Stop me if you've heard this before. You pay $20 to cover the pizza order for your friends. None of them have cash on them, or at least nothing smaller than a $20, so they promise to get you back. The money never comes.

College is full of moments like this. Whether it's splitting a bill, getting paid back for booze or cover at a dorm party, or buying and selling old DVD's and dorm furniture. If you're anything like me though, you hardly ever have cash on hand, and most of your friends don't either. Luckily, the days of unpaid debts are over thanks to Square.

If you haven't heard about it, Square is a mobile payment startup founded by some of the same people who brought you Twitter, and it's incredible. Simply sign up for a free account, and they'll mail you a free (!) credit card reader tha plugs into the headphone jack of your iPhone, iPad, or Android device. Once you have everything you need, simply type in what you want to charge your friend on the app, and have them swipe their credit or debit card. They even get a receipt!

Of course, there are some drawbacks. You will pay a 2.75% processing fee on all transactions, so you'll either need to eat that cost yourself or build it in to the charge, which runs the risk of pissing off your friend. In my experience the reader often takes a few swipes to work properly, but that's not really a dealbreaker. If you're concerned at all about privacy though, it's been reported that the reader can be hacked to act as a credit card skimmer, but if you're the one actually accepting the payments you won't need to worry.

Overall, the benefits far outweigh the drawbacks. I personally hope these things become as ubiquitous as cellphones, as I hate feeling like a bum when I don't have cash, probably more than I hate being saddled with a full bill by my cashless friends. This is a fantastic, free system that most college students could use on a weekly basis, and there's no good reason to delay signing up.