RFID / NFC technology is a great way to interact with projects. NFC (Near Field Communications) is a way for two devices very close to each other to communicate. Sort of like a very short range bluetooth that doesn't require authentication. It is an extension of RFID, so anything you can do with RFID you can do with NFC. Because it can read and write tags, you can always just use this for RFID-tag projects. For a good example of how these boards can be used, check out Becky Stern's Babel Fish project on the Adafruit Learning System.
Adafruit's RFID / NFC boards were designed by RF engineers using the best test equipment to create a layout and antenna with 10cm (4 inch) range, the maximum range possible using the 13.56MHz technology.
Learn more about RFID / NFC products and projects on the Adafruit Learning System.