weekday, a FORTRAN77 code which determines the day of the week corresponding to a given date; for instance, the battle of Hastings, on 14 October 1066 (Julian Calendar!), was a Saturday.
The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
weekday is available in a C version and a C++ version and a Fortran90 version and a MATLAB version and an Octave version and a Python version.
analemma, a FORTRAN77 program which evaluates the equation of time, a formula for the difference between the uniform 24 hour day and the actual position of the sun, creating data that can be plotted by gnuplot(), based on a C program by Brian Tung.
calendar_nyt, a FORTRAN90 library which shows the correspondence between dates and the New York Times volume and issue number;
calendar_rd, a C++ program which computes the representation of a given date in a number of calendrical systems, by Edward Reingold, Nachum Dershowitz
CALPAK, a FORTRAN90 library which makes various calendar calculations;
DATES, a dataset directory which contains lists of dates in various calendar systems.
DOOMSDAY, a FORTRAN77 library which is given the year, month and day of a date, and uses John Conway's doomsday algorithm to determine the corresponding day of the week.
TEST_VALUES, a FORTRAN77 library which supplies test values of various mathematical functions.