calendar

A month at a time, Mondays first. The grid always shows whole weeks, so days borrowed from the neighbouring months appear faded at either end. The date math is done in the open - leap years land February 29 exactly when the rules say (2024 yes, 1900 no) - and the calendar covers years 1 through 9999. Until it learns the real date it opens on January 1970.

Using

• flip turns one month by default; give it a number to jump farther, forwards or back.
• Go straight to any year and month - the month by number or by name.
• today jumps to the current month and marks the day; the mark disappears when you flip away.
• Tap a day to pick it. A day the month does not have is refused.
• The month you were viewing is remembered.