It can act as a reader. It can eavesdrop on a transaction between another reader and a tag. It can analyze the signal received over the air more closely, for example to perform an attack in which we derive information from the tag's instantaneous power consumption. It can pretend to be a tag itself. It is also capable of some less obviously useful operations that might come in handy for development work. (from http://www.cq.cx/proxmark3.pl)

There is a community website and a reference manual available thanks to a group of volunteer enthusiasts.

The kit include:

• fully assembled, programmed and tested Proxmark3 [PM3],
• powered and flashable by USB,
• low frequency antenna board (125 /134 kHz) [LFA],
• Ultra short Hirose cable to connect PM3 and LFA [LFA cable],
• USB cable for connection to computer [USB cable],
• fancy manual incl. "High Frequency Antenna HowTo" [manual],
• Hirose cable to make a high frequency (13.56 MHz) antenna [HFA cable]
• Hirose cable to make a HFA* and to connect the LFA* at the same time [MM cable]

*HFA: High Frequency Antenna
*LFA: Low Frequency Antenna