I’d like to mention GitHub - davedelong/time: Building a better date/time library for Swift by @davedelong which is all about using Swift type system so one don’t fall into traps about dates, timestamps, calendars and locales.
It is properly documented and the api is made to guide you toward correctness. 2k stars and properly tested AFAIR.
When I can’t import this I’m jealous of Java/kotlin and their provided time package with LocaleDate and friends. I think the next foundation should provide at least some of those abstractions in a similar easy to use api.