r.ros(1grass) on Linux
The text bd1fc2b9d552, as Debian 8 (Jessie) shipped it.
Generates three, or four raster map layers showing 1) the base (perpendicular) rate of spread (ROS), 2) the maximum (forward) ROS, 3) the direction of the maximum ROS, and optionally 4) the maximum potential spotting distance.