With this app you make actual and direct contributions to OpenStreetMap. There is no third party in-between the app and OSM infrastructure.
Editing OpenStreetMap anonymously is not possible. Any changes you make (and their date and location) are attributed to your OSM user account and publicly visible on the openstreetmap.org website. Because Every Door should only be used for on-site survey, this reveals where and when you have used the app.
The app does not share your GPS location with anyone. It is used to focus the map around your location, optionally downloading map tiles.
If you have any questions, ask Ilya, the author.
Portions of this text were adapted from StreetComplete’s statement.