The proxmark3 is a powerful general purpose RFID tool, the size of a deck of cards, designed to snoop, listen and emulate everything from Low Frequency (125kHz) to High Frequency (13.56MHz) tags. This repository contains enough software, logic (for the FPGA), and design documentation for the hardware that you could, at least in theory, do something useful with a proxmark3.
You can download it from the following link: https://packetstormsecurity.com/files/download/142802/proxmark3-3.0.0.tar.gz
Source: https://packetstormsecurity.com/files/142802/Proxmark-3.0.0.html