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CalendarForge

The sky keeps two clocks that don’t divide evenly — so every calendar drifts, by an amount you can do the maths on.

The two-clock problem

The sun’s year is about 365.24 days. The moon’s month is about 29.53 days. Neither divides evenly into the other — 12 moon-months make only ~354 days, about 11 days short of a solar year. So every calendar ever built is a compromise, and the amount it slips against the seasons is not a mystery: it is subtraction and division you can do yourself.

☀️ Solar (Gregorian). Ignores the moon, tracks the sun. A clever leap rule (4 / 100 / 400) keeps it within a day of the seasons for thousands of years.
🌙 Lunar (Islamic / Hijri). Follows the moon exactly, so it drifts ~11 days earlier every solar year — Ramadan slides through all the seasons in about 34 years.
🌙☀️ Lunisolar (Hebrew / Chinese / Tết). Keeps lunar months but adds a whole extra month every few years (the 19-year Metonic cycle) so it stays with the seasons. The best of both.

Everything runs on your device — no calculator, no internet, no accounts.

Meet the crew — the four calendar-keepers

Sol keeps the sun’s year and tunes the leap rule so the seasons never slip — a day’s error takes millennia.
Luna follows the moon faithfully, month by month, and lets the seasons drift — that is the honest cost of a pure-lunar calendar.
Metone (mentor) knows the 19-year secret: slip a whole extra month in seven years out of nineteen, and the moon and the sun come back in step.
Drift is the quiet accountant, adding up the fractions of a day nobody notices until, centuries later, the calendar is ten days out.

Painted friends + storybooks are coming soon.