p0f(1) on Linux
The text a3c27434e79d, as Debian 8 (Jessie), Debian 7 (Wheezy), Debian 6.0 (Squeeze), Debian 5.0 (Lenny) shipped it.
identify remote systems passively
Flags it lists
-
-0 -
-A -
-C -
-D -
-F -
-K -
-M -
-N -
-O -
-Q -
-R -
-T -
-U -
-V -
-X -
-d -
-e -
-f -
-i -
-l -
-o -
-p -
-q -
-r -
-s -
-t -
-u -
-v -
-w -
-x