Day One is a journaling and notes app for iPhone, iPad, Mac, Android and the web. Entries can include text, photos, video, drawings and audio. The vendor's website mentions end-to-end encryption, without describing its scope, and automatic backups. It is a personal app for each platform, not self-hosted software.
Day One belongs to Automattic Inc., headquartered in San Francisco, United States. The privacy policy names no hosting countries. It states that data of users in the EU may be used or accessed outside the European Economic Area, with European Commission standard contractual clauses for those transfers. Because the parent is a US company, US law may apply to data it controls, regardless of server location. A European organisation should weigh this for personal or confidential content.