In macOS 14, Apple removed two "easter eggs"

While the 4.4BSD Calendar program is still included, they removed the data directory at /usr/share/calendar which previously included some fun "easter egg" text files including calendar.birthday, calendar.history, calendar.lotr, and calendar.music.

If you happen to care you can restore the files in this repository into /usr/local/share/calendar:

https://github.com/freebsd/calendar-data

They also removed the "Puff of Smoke" animation that was still present through macOS Ventura whenever dragging items off of application toolbars to remove them. It is notably deprecated here:

https://developer.apple.com/documentation/appkit/nsanimationeffect?language=objc