Generate fractals resembling clouds, planets and starry skies. More information: https://netpbm.sourceforge.net/doc/ppmforge.html.
ppmforge > path/to/image.ppm
ppmforge -night|clouds > path/to/image.ppm
ppmforge -mesh 512 -dimension 2.5 -xsize 1000 -ysize 1000 > path/to/image.ppm
ppmforge -tilt -15 -hour 12 > path/to/image.ppm