You may know the date of your birthday, but you may not know what day it was! Do you know whether the French Revolution started on a Monday or a Friday? What day will 2.2.2044 be? Feed Chronos any date from 1200 BCE to 2100 CE, and you will get its weekday.
Moreover, what is the current Islamic year? or the current Bengali year? Or what were the Islamic and Bengali years in 1759? Chronos is able to provide you with this kind of answers too, and lets you add/remove other Eras besides the default (Bengali and Islamic) ones.
Eventually you may get the day of the week of Christmas and Epiphany from 100 CE to 5000 CE, and retrieve the dates of Easter Sundays from the first Century up to 5000 CE.