Calendar

The calendar extension provides functions to convert dates between different calendars, such as Gregorian, Julian Day Count, Unixtimestamp, French Revolutionary, Jewish, and others.

<?php

    $julian_date = gregoriantojd($m, $d, $y);
    $french = jdtofrench($julian_date);

    echo $french;

?>

Documentation

See also Event Calendar with PHP.

Related : DateTime, DateInterval