Hebrew calendar
Yahrzeits, Hebrew birthdays, and anniversaries are tracked on their Hebrew dates, and reminders are Shabbos- and Yom-Tov-aware — they send erev, not on the day. No mainstream CRM does this.
Store the Hebrew date of passing as the source of truth; the next Gregorian observance is computed automatically, including Adar in leap years.
A reminder that would land on Shabbos or Yom Tov moves to erev — the day before — automatically.
Each yahrzeit links to the family, so a reminder becomes a reason to reach out.
The same Hebrew/English dating powers your receipts and letters.