CalendarKit is a high quality open source implementation of iOS Calendar day view UI that can be easily embedded into an iOS app. For example, multiple university schedule apps have been created with it and it’s already quite popular on GitHub (more than 2 thousands stars).
The library is also very helpful to anyone interested in learning how to build an own UI library or learn more about date and time processing on Apple platforms.
The library has a few mentions in the iOS-related newsletters as well as a dedicated StackOverflow tag: Newest 'calendarkit' Questions - Stack Overflow
It’s actively maintained and supported for all the major iOS versions.