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