Day One is a personal journaling app available for Android, macOS and iOS devices.

Some features include: data syncing with multiple devices; end-to-end encryption, Markdown authoring of entries; location, weather, date, time, and other automatic metadata; quick entry menu bar (Mac only); and reminders.

[8] On February 4, 2016, the developers, Bloom Built, introduced Day One 2 for Mac and iOS, citing the release as a full app rebuild.

The update introduced a visual overhaul and new features such as multiple journals and photos.

[9] On June 12, 2017, Bloom Built added end-to-end encryption to Day One 2 after two years of development.