In Java, Joda-Time was a third party library for ages. It was the dominant date-time lib for enterprise development. Then, it was standardised and added to the stdlib: java.time (JSR-310). The Joda-Time project lead, Stephen Colebourne, ran the standardisation process. It was well received by most, even the breaking API changes that SC was adamant were flaws in the original Joda-Time API. I can vouch for it: Both Joda-Time and the java.time libs are excellent. (In my job, I regularly need to perform complex date-time transformations, including time zones.)

I have also used Howard Hinnant's C++ date-time lib: https://github.com/HowardHinnant/date It is also very good. (He was the guy behind move semantics in C++ 11.)

In Python, the stdlib has a function to get UTC now, that does not include UTC timezone... so it weirdly and surprisingly acts like local time zone! There is endless shit-posting about it. I feel bad for Guido van Rossum et al. To be fair, the original Java date-time lib was horrible, so Joda-Time was created. And JDBC (Java database) dates are still horrible.