A binnacle is the stand that houses a ship's compass: a pedestal with a bowl, holding a card that stays pointing north however the ship turns and undulates beneath it.
Binnacle is an instrument of that kind for a phone. A golden pendulum pointer hangs on a pivot above a stone bowl inlaid with compass roses, and it corresponds to the real world: to gravity, to the earth's magnetic field, and to how you hold it. Tilt the phone and the pendulum swings on its pivot. Turn around and the card holds north while everything else moves.
It is a soft fascination toy rather than a tool, and it does not explain itself all at once. Some of what it does has to be found.
A few plain facts:
Free, with no advertising and no purchases of any kind.
It collects nothing. No accounts, no analytics, no third party code. It does not ask for internet access, so it has no way to send anything anywhere.
It needs a gyroscope, an accelerometer and a magnetometer, because a compass that did not read them would be a picture of a compass.
The first launch spends a few seconds building its renderer before the scene appears, and goes on building quietly for a little while after that. It happens once per device.
A golden pendulum hangs over a stone bowl and answers to the real world.