Iain Sinclair's CardSharp Credit Card Folding Knife(£15) is a svelte knife and folds into a card to fit in your wallet. It weighs just 13 grams, is only 2mm thick and features a stainless steel blade with a healthy 65mm cutting edge and a short serrated edge on the opposite side. When folded, a built-in sheath prevents you from accidentally touching the sharp blade. Check out the video, you can see how it does fold/unfold. It will start shipping from January for £15($23) and and can be pre-ordered.