Ruby-calendar includes the following modules.

Calendrical Calculations module:
  This module supports the following calendars:
    Gregorian (current civil), Calendar week (ISO), Julian (old
    civil), Islamic (Moslem), Hebrew (Jewish), Mayan, French
    Revolutionary, Old Hindu, Achelis', Coptic, Ethiopian, Jalaali
    (incomplete), Kyureki (Japanese traditional with CE) A "Getdate"
    module

Getdate module:
  This module provides a method which creates a Time object reflecting
  the given representation of dates and times.  An "Sdn" module

Sdn module:
  This is an interface to the Scott E. Lee's SDN package.
  This module supports the following calendars:
    Gregorian, Julian, French Republican, Jewish

Author:	Tadayoshi Funaba <tadf@funaba.org>
WWW:	http://www.funaba.org/en/calendar.html#calendar