You must have spotted at least one QR code by now. If not, then you are a certifiable alien from Mars. QR codes are quite the rage. We have them on everything from food labels to car bumpers. And yes, tattoos too! QR codes are definitely mainstream now, given a boost up the use of smartphones and intelligent scanning apps that reside in them. So, here are five more web apps which show us how QR codes have gone conventional.