Sleep cycle calculator, basically calculates the best time to wake up if you are going to sleep now. Based on the idea that sleep runs in ~90 minute cycles and waking up between them feels terrible.
Shows 7 wake-up windows (1–7 cycles, 1.5h–10.5h of sleep). Updates every minute. Click the alarm icon on any card to download an .ics file you can import into any calendar app.
Plain HTML, CSS, JS. One Google Font (Nunito). Nothing else.