Coo

I have a baby of my own, and for a while the log of our days was a piece of paper. My girlfriend and I wrote down every feed and every diaper on it — or I typed them into the notes on my phone, and then gave her the briefing at three in the morning.

I wanted an app to replace the paper. I could not find one on the Play Store that had all of it in one place, for free. So I built it.

The part I built it for is free, and stays free: logging feeds, diapers, sleep and pumping, and sharing that log with your family. The smart extras are Premium — a sleep prediction, logging by voice or text with AI, a written summary of the night and a weekly summary. Everyone gets all of it free for the first seven days. After that you can pay for a month, a year, or once and forever — or simply stay on the free tier, for as long as you like.

Feeds: breastfeeding with a timer per side and a switch between them, or a bottle of formula or expressed milk, in ml or oz. Diapers: wet, dirty or mixed. Sleep: naps and night sleep, with a timer. Pumping: a timer and the amount.

The Today screen is the briefing, done for you: how long the baby has been awake or asleep, and the last feed, diaper, sleep and pump at a glance, with quick-log tiles and the day’s timeline underneath. The Log screen draws each day as a rhythm band — sleep filled in, feeds as long as they took, diapers and pumps marked, quiet hours shaded — and a tap opens it zoomed to six hours with every item labelled.

During your quiet hours (22:00 to 07:00 unless you change them), or whenever the phone is in dark mode, it switches to a warm amber night palette with big buttons, built for one hand in the dark. Anything can be edited, logged after the fact or deleted with an undo, and if an entry looks like a duplicate or isn’t plausible, Coo asks first. It speaks English, German, French, Spanish, Italian, Polish and Dutch.

Both parents sign in with their own Google account and share one log between their phones — the second is invited by a link, and sync keeps working offline. There is a PDF report to take to the paediatrician, and you can log from a Wear OS watch. All of that is free.

A log about a child is health data, so it stays home. Coo works fully offline, needs no account until you share, keeps the log on the phone, and carries no ads, analytics or trackers. Android backup is switched off for it on purpose.

When you share, the server is how phones catch up with each other, not the place the data lives. The sync protocol is built around that: an outbox of local changes, hybrid logical clocks to order edits made on different phones, and per-household sequence numbers so a phone asks only for what it missed. It runs on my own server at Hetzner in Nuremberg — no Firebase.

The app is .NET 10 MAUI around a pure, hexagonal domain model. Every increment is specified and agreed before any code, and verified on a real Pixel 10 before it counts as done, with more than 500 automated tests underneath.