This program lacks any documentation at all. So to anybody actually trying to use this, here goes:
It expects a minimum of 2 arguments:
fti2svg infile.fti outfile.svg
You can pass it multiple .fti files and it will composite them from the bottom up:
fti2svg infile1.fti infile2.fti infile3.fti outfile.svg
It also does no error checking and will happily overwrite your files with no warning.