The PN531 and its replacement the PN533 chip support direct USB communication. They make it easy to build NFC readers. No micro-controller is necessary to handle USB frames and no driver development is required. It is feasible to construct a NFC/RFID reader of the size of an ordinary USB dongle. It only needs one chip and a miniature antenna. Example product is the SCL3711; its predecessor the SCL3710 is shown above.
A list of compatible NFC-dongles can be found on the compatibility page.