Date::Convert::French_Rev can convert from / to French Revolutionary Calendar.

SYNOPSIS

use Date::Convert::French_Rev;
Converting from Gregorian (or other) to Revolutionary
$date=new Date::Convert::Gregorian(1799, 11, 9);
convert Date::Convert::French_Rev $date;
print $date->date_string, "n";
print $date->date_string($format), "n";
Converting from Revolutionary to Gregorian (or other)
$date=new Date::Convert::French_Rev(8, 2, 18);
convert Date::Convert::Gregorian $date;
print $date->date_string, "n";