STEM
CalendarForge
Why does Tết move? Why does Ramadan slide earlier every year? Because the sun and the moon keep two clocks that don’t divide evenly — and you can do the arithmetic. Build a solar, lunar, and lunisolar calendar, predict how far each one drifts against the seasons, then watch the days pile up on a drift chart. Real, tiny, deterministic maths — no internet. Ages 9–14.
#4a5bd0 Distributed-narrative cast
Meet the cast
CalendarForge's crew ARE the four keepers of a calendar — the cast IS the curriculum: each character's habit IS one calendar's compromise with the sky. Sol keeps the sun's year and tunes the leap rule so the seasons never slip; Luna follows the moon faithfully and lets the seasons drift ~11 days a year (the honest cost of a pure-lunar calendar); Drift is the quiet accountant, adding up the fractions of a day nobody notices until, centuries on, the calendar is ten days out. Mentor Metone 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 — which is exactly why Tết, Ramadan and Easter move the way they do. Painted portraits + storybooks are a tracked follow-on (R-WEB-CLONE-SPAWN-TRACKED); a text-only crew + flat, deterministic on-device maths ship now — nothing leaves the device.
Sol
Keeps the sun's tropical year and tunes the leap rule (4 / 100 / 400) so a day's error against the seasons takes millennia to build
Luna
Follows the moon month by month; a pure-lunar year is ~11 days short of a solar year, so her dates drift earlier and earlier — the honest cost of tracking the moon alone
Metone
(Mentor) Knows the Metonic secret — 19 solar years ≈ 235 moon-months — so seven years in nineteen get a 13th leap MONTH to keep a lunisolar calendar with the seasons
Drift
The quiet accountant who adds up the fractions of a day nobody notices, until centuries later the calendar is ten days out and needs a correction
What's inside
Learning goal
Why does Tết move? Why does Ramadan slide earlier every year? Because the sun and the moon keep two clocks that don’t divide evenly — and you can do the arithmetic. Build a solar, lunar, and lunisolar calendar, predict how far each one drifts against the seasons, then watch the days pile up on a drift chart. Real, tiny, deterministic maths — no internet. Ages 9–14.
Question kits
16 curriculum-aligned kits × 25 questions = 400 questions per app, mapped to recognized standards.
On-device AI mentor
FoundationModels-powered hints, feedback, and adaptive difficulty — all running locally.
Mentored by Metone — on-device AI, no data leaves the device.
How CalendarForge handles your kid's data
- ✅ All progress, settings, and AI-generated content stays on the device
- ✅ No analytics, no tracking, no third-party SDKs
- ✅ No ads, no in-app purchases — you pay once
- ✅ No personal information collected from children — in line with COPPA (updated by the 2026 FTC amendments)
- ✅ Parental controls + session limits + content filters built in
CalendarForge runs on ForgeKit — the open-source Swift Package Manager framework that powers every Spark & Anvil app. ForgeKit ensures consistent accessibility, COPPA compliance, and design language across the portfolio, so your kid's progress and preferences feel coherent across every app they touch.
Coming to the App Store
CalendarForge is in active development. Email us to hear when it ships — no marketing, no spam, just a one-shot launch announcement.
Email me at launch