Kalendar for Mac

From Sci-Fi Hi-Fi:

Kalendar is a small Cocoa application which uses Ronald Mallen's algorithm to calculate the Gregorian calendar date of Orthodox Easter. For those who aren't familiar with the issues surrounding the calendar and the Orthodox Church, understanding this program's purpose requires a bit of background.

Prior to 1582, both the Easter and Western churches used the Julian calendar system, which had a problem in that it inaccurately calculated the solar year at 365.25 days. As a result of this miscalcuation, the Julian calendar slipped about 11 minutes out of sync with the actual solar year every year, such that it cumulatively slipped a day approximately every 131 years. The need for reform was recognized, and in 1582 Pope Gregory XII finalized a correction of the calendar known today as the Gregorian Calendar. The Eastern Orthodox church, however, did not even think about adopting this reform until 1923, and even then the change met with so much resistance that even to this day, the Orthodox calculate the date of Easter using the Julian Calendar.

This program performs two principle functions: first, it takes a year as input and runs it through an algorithm developed by Ronald Mallen of the Astronomical Society of South Australia (http://www.assa.org.au/edm.html); then it adjusts the resulting Julian date to Gregorian with a little help from some nice code by Scott E. Lee (http://www.scottlee.net/).