Adafruit has turned its popular Adafruit PN532 breakout board into a shield - the perfect tool for any 13.56MHz RFID or NFC application. The Adafruit NFC shield uses the PN532 chip-set (the most popular NFC chip on the market) and is what is embedded in pretty much every phone or device that does NFC. This chipset is very powerful, and can pretty much do it all, such as read and write to tags and cards, communicate with phones (say for payment processing), and 'act' like a NFC tag.