Mayan Calendar Tools: Web tools for working with the Mayan and Gregorian Calendars.
The Maya calendar is a system of distinct calendars and almanacs used by the Maya civilization of pre-Columbian Mesoamerica. (cite: wikipedia.org)
Maya Civilization: The Maya calendar in its final form probably dates from about the 1st century B.C., and may originate with the Olmec civilization. It is extremely accurate, and the calculations of Maya priests were so precise that their calendar correction is 10,000th of a day more exact than the standard calendar the world uses today. (cite: civilization.ca)