The Gregorian calendar is pretty solid actually. Other than a leap second every few years, it’ll stay in sync for a few thousand years. You can easily calculate all leap days in a one-liner.
365 is semi prime, so we could do a 5 day week, but that’s pretty minor in the grand scheme of things. There isn’t a lot to improve on the Gregorian calendar
- leap days only coming at the end of the year, not in the middle
- 5 day week
- 73 day months
- 30 day months with 5 non month days
Don’t get me started on timezones