wekan/packages/wekan-fullcalendar/fullcalendar/demos/php/get-timezones.php

<?php

//--------------------------------------------------------------------------------------------------
// This script outputs a JSON array of all timezones (like "America/Chicago") that PHP supports.
//
// Requires PHP 5.2.0 or higher.
//--------------------------------------------------------------------------------------------------

echo json_encode(DateTimeZone::listIdentifiers());