Timestamps, cron expressions, timezones and durations.
Read a cron expression in a sentence, see the next six times it fires in your own zone, and start from a preset if the fields are the part you never remember.
Pick a time in one zone and read it in all the others at once, with the offsets shown and daylight saving handled by the browser's own database.
Turn a Unix timestamp into ISO, UTC and your own time zone at once, or paste a date and read the epoch back. Seconds and milliseconds both.