P0f is a tool that utilizes an array of sophisticated, purely passive
traffic fingerprinting mechanisms to identify the players behind
any incidental TCP/IP communications (often as little as a single
normal SYN) without interfering in any way. Version 3 is a complete
rewrite of the original codebase, incorporating a significant number
of improvements to network-level fingerprinting, and introducing the
ability to reason about application-level payloads (e.g., HTTP).

To build and install the optional signature and API tools, specify
TOOLS=yes to the SlackBuild, for example

  TOOLS=yes sh p0f.SlackBuild
