A calendar that knows whose appointment it is.
Every family member has a colour, and that colour is the same everywhere in the app. Open the month view and, before you read a single title, you already see whose week is crowded.
Recurrence that behaves the way you expect
Daily, weekly, monthly and yearly, with intervals, weekday and month-day selectors, a count or an end date. When you edit or delete an event in a series, the app asks what you mean — this occurrence, this and everything after it, or the whole series — and all three do exactly what they say.
Recurrence across clock changes
A nine o'clock meeting stays at nine o'clock after the switch to summer time. An all-day event is a date, not an instant, so it does not slide a day when you travel. That sounds like a detail right up until a birthday lands on the wrong day.
Four views
Month, week, day and agenda. Drag an event to move it, drag its edge to stretch it.
Quick add
Type "dentist tuesday 3pm" and you get a real event, on the right day, at the right hour.
Export and import
A calendar exports as an ICS file, and every calendar app opens that format — so the family's events reach the people who do not have an isna account. ICS import works too, with duplicate detection on re-import, so a calendar from another app moves across in one step.
A live subscription is being built
A calendar that refreshes itself on your phone, rather than a file you export now and then, is what is in progress — see the roadmap. Until it lands, nothing on this site says "subscribe to the calendar", because that is not true yet.
Reminders
Per event, at any lead time, by email or as a browser notification. Move the event and the reminder moves with it.
Start with the one deadline you cannot afford to miss.
Set your family up in two minutes. Thirty days of everything, and it does not ask for a card.