CardSharp

From Uncrate:

Want to carry a knife but don't feel like adding any extra bulk to your already crowded pockets? Check out the CardSharp (£15; roughly $23). Thanks to its ingenious folding design, the CardSharp is the same size as a credit card, yet offers a 65mm stainless steel blade, and folds up securely for travel. A bit of advice: make sure it's not in your wallet the next time you're heading into the TSA line.