Lotti allows you to collect potentially sensitive information about yourself, your life, your health, all on your own devices and without collecting the data in a centralized place. No data is shared with anyone, which is not even possible without collecting it in the first place.
Lotti is open-source software, which allows anyone to verify that the claims above are indeed accurate. The aim of the project is to make the collection of data in a private journal entirely private and trustworthy. Anyone is encouraged to suggest improvements and raise concerns about how data is stored and handled.
Multiple devices can be synced via a user-provided email account through which information is exchanged, with encryption where the key is exchanged by generating and scanning a QR code.
Currently, the data on device is not encrypted. This is supposed to change going forward. In any case, it is highly encouraged to encrypt your devices anyway.
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When participating in beta testing via Apple's TestFlight, it is required to send an email to the author providing your Apple ID.