SinFP is a new approach to OS fingerprinting, which bypasses limitations that nmap has. It only requires one open TCP port, sends only fully standard TCP packets, and limits the number of tests to 2 or 3.
You can download it from the following link: https://packetstormsecurity.com/files/download/51711/SinFP-2.04-1.tar.gz
Source: https://packetstormsecurity.com/files/51711/SinFP-2.04-1.tar.gz.html