# for pkg in $(prt-get listinst); do pkginfo -l $pkg; done | sort -u > /tmp/db
# cd / # find * \( -type d -printf '%p/\n' -o -print \) | \ egrep -v "^(lost\+found|proc|sys|dev|run|tmp|root|home|boot|lib/firmware|lib/modules|usr/ports)" | \ sort > /tmp/fs
# comm -23 /tmp/fs /tmp/db | less
Maybe you want to have a clean system, and just can remove some garbage files.