Ask HN: What is the best Date and Time library (in any language)?

Date and time and time zones are notoriously hard to handle correctly. What libraries handle time the best? Which ones make it the most difficult to shoot yourself in the foot? Which language has the best standard library date/time module?

Various dimensions for comparison include: - handling of timezones - handling of durations - handling of other date/time arithmetic - formatting and parsing - explicitness for handling time with timezones vs. UTC