Seratus
The OS for your whole life.
Health, finances, calendar, and habits. In one place you actually own. Works offline. No subscription. No lock-in.
Open source · Runs in your browser · Your data stays yours
Period tracker
Not every cycle is 28 days.
Seratus is designed for the cycle you actually have. Long cycles, short cycles, gaps, irregular timing, birth control, and times when you are not cycling can all be tracked without being treated as data errors.
Predictions are weighted toward your recent history, so the app adapts to your pattern instead of forcing a textbook average onto it.
Your data is yours. Everything lives in your browser. Export to JSON anytime. No account, no server, no one else can read it.
Works offline. Load it once and it runs without internet. Nothing breaks when your connection does.
No subscription. Ever. Free to use, free to keep. No credit card, no trial, no plan to monetize you later.
Open source, noncommercial. Fork it, adapt it, build on top of it for personal use. Attribution required. Selling it or using it commercially is not permitted.
100 years. The calendar starts on your birthday and runs for a century. Plan slow.