An alternate calendar system briefly used by republican France. It had 360 days per year with 5 or 6 “intercalary” or leap days between years. It had 12 months of 30 days, which were comprised by 3 weeks of 10 days. Every day of the year had a unique name: a common plant, animal, mineral, or tool/equipment (ie January 31 was “Broccoli” and May 4 was “Silkworm”).
YSK because it’s an interesting alternative to the Gregorian calendar and the occasionally-proposed 13 month calendar.
Though it did have some problems such as starting in late September (very unusual for a calendar) and not having a robust leap-year system.
They did not have a 31st day and neither did they have a January. Rather, the day that we call January 31 was the 12th day of Pluviôse and also had its own name “Broccoli”