The Christian year by the 1928 Book of Common Prayer, for iPhone and iPad.
Email support@ryan.freckleton.us. Questions about how a day is kept are welcome too; the app shows its reasoning, and the reasoning quotes the book.
The app collects no data. It has no account, no ads, no analytics, and no network connection. Everything it shows is built into the app, and nothing leaves your device.
The calendar rules, Collects, Epistles, and Gospels are from the Book of Common Prayer (1928), which is in the public domain. The Epistles and Gospels are the King James Version as the Prayer Book prints them. Liturgical colours are customary, after the American Missal.