Wren

What's in it

• Sleep, nursing, bottles, pumping, solids and diapers, each one a tap or two, with the four you reach for most under your thumb.
• Logging without opening the app: home-screen and Lock Screen widgets, Controls, Quick Settings tiles, Siri, and the watch.
• A timer you can start late and fix afterwards.
• The Timeline by day, week and month, each with its own numbers underneath.
• Moments: keep any moment you want to remember, with a photo or a few words, and mark the firsts if you like.
• Weight, length and head size on public growth curves. Medicines with a “not before” for an as-needed dose, and temperatures and symptoms kept together while a child is unwell.
• Export everything, any time, as a file you can open anywhere.
• Free to use. Wren Household, an optional subscription, adds a second device and more, a second child and more, the watch, a colour for each child, and the PDF for the pediatrician.

What was hard about it

Most of Wren's logging happens where the app is not running. A feed started from a home-screen widget, a Control, the Lock Screen or a watch has to land in the same record as one started inside the app — which means a store both sides can write to, and a timer the system will not quietly kill. On Android that means surviving Doze, a force-stop, and the task-killers some manufacturers ship.

Sharing was the other half. Updates and photos travel between the devices in one household through a relay we wrote, which holds each one only until every device has it and then forgets it. Nothing piles up there to be lost later.

Then the paperwork, which is most of what shipping actually is: a French encryption declaration, EU trader status, health declarations on Play, a regulated-medical-device declaration for Apple, and a fix we sent upstream to the purchase plugin the app is built on.