The calendar has many options with a standard monthly interface, including sunrise, sunset, and Moon phases.

CalSKY - The worldwide interactive online astronomical/space calendar and calculator - for friends of astronomy, as well as astronomers.

Explains the difference between millenium and year 2000 as the absence of a year zero.

Lots of time and date related information, such as yearly and monthly calendars, counters, countdown, and the world clock which shows the current time in cities all over the world.