* The Gregorian calendar is the most widely used calendar in the world today. It is a solar calendar, which means that it is based on the Earth's orbit around the Sun. The Gregorian calendar has 365 days in a year, with an extra day (leap day) added every four years to account for the fact that the Earth's orbit is not exactly 365 days long.
* The Julian calendar is the predecessor of the Gregorian calendar. It was introduced by Julius Caesar in 46 BC and was used throughout most of Europe until the 16th century. The Julian calendar is also a solar calendar, but it has a few minor differences from the Gregorian calendar. For example, the Julian calendar does not have a leap day every four years; instead, it has a leap day every three years.
* The Chinese calendar is a lunisolar calendar, which means that it is based on both the Earth's orbit around the Sun and the phases of the Moon. The Chinese calendar has a 12-year cycle, with each year being associated with a different animal.
Lunar calendars
* The Islamic calendar is a lunar calendar, which means that it is based on the phases of the Moon. The Islamic calendar has 12 months, with each month beginning on the day of the new moon. The Islamic calendar is used in many Muslim countries around the world.
* The Hebrew calendar is a lunisolar calendar, which means that it is based on both the Earth's orbit around the Sun and the phases of the Moon. The Hebrew calendar has a 19-year cycle, with each year being either 12 or 13 months long. The Hebrew calendar is used in Israel and by many Jewish communities around the world.
Other types of calendars
* The Mayan calendar is a complex calendar that was used by the Maya civilization of pre-Columbian Mesoamerica. The Mayan calendar is based on a combination of solar, lunar, and Venusian cycles.
* The Aztec calendar is another complex calendar that was used by the Aztec civilization of pre-Columbian Mesoamerica. The Aztec calendar is based on a combination of solar, lunar, and agricultural cycles.