Reading plans, paydays, sunsets, full moons, home maintenance, daily puzzles. Pick one, tap Add, and it shows up in Apple Calendar on its own. No app to install, nothing to sign up for.
A subscribed calendar is a live link. Your phone checks it about once a day and adds new events automatically. You can't accidentally edit it, and deleting it removes every event at once (Calendar › Calendars › ⓘ › Delete Calendar).