fitarchive is a private, self-hosted tool. It downloads the health and fitness data of its operator from the Google Health API and stores it in a database on the operator's own computer. A dashboard and analysis tools that run on the same computer read from that database.
fitarchive is not a public service. It has a single user, who is also the person who runs it. There is no sign-up, and the tool is not offered to anyone else.
fitarchive asks for read-only access to the Google Health data of the account that signs in: activity, heart rate and other health metrics, sleep, profile and settings. It copies this data to a local database. It does not change any data in the Google account and does not pass data on to anyone.
The privacy policy describes this in detail.