The 'libkal' library provides support for converting dates between various calendar systems (currently only julianic, gregorianic, arabic and jewish ones) and some more related stuff. . The basic idea of this library is, that any date in any calendar system can be converted to a single number, which express the number of days since some fixed date in the past. libkal uses the so-called 'julianic date'(jd), that is used in Astronomy (not exactly).
