This is a custom firmware written for the proxmark3. It extends the currently available firmware (revision 2.3.0) to support brute force attacks against proximity card access control systems.
You can download it from the following link: https://packetstormsecurity.com/files/download/140979/proxmark3-1.6.9.tar.gz
Source: https://packetstormsecurity.com/files/140979/Proxmark-Iceman-Fork-1.6.9.html