Kevin Le

In Vietnamese families, the dates that matter most move every year. A grandparent s death anniversary, T t, the full moon offering: they all follow the lunar calendar, so they land on a different day of the solar calendar each year. Someone in the family has to remember, and tell everyone else. For families living abroad it is even harder.

Nh t Nguy t is the app we built for that.

What it does

• Lunar reminders that repeat correctly. Set a death anniversary once, and it lands on the right solar date every year, including leap months.

• Family groups. Shared reminders, a plan for each occasion, comments and a photo album per event.

• Everywhere you look. Home-screen widgets on Android and iOS, Wear OS and Apple Watch, Google Calendar sync, and a web version.

• Living abroad? Choose whether the calendar follows Vietnam time or your local time.

• Three languages: Vietnamese, English and Chinese.

In Vietnam the lunar calendar is not folklore. It s a working tool. Families use it to:

• remember ancestors death anniversaries, which fall on a lunar date

• pick dates for weddings, moving house or opening a shop

• prepare offerings for the 1st and 15th of every lunar month

Today this information is spread across ad-heavy sites, paper almanacs and one relative who just knows . Most of it has no sources, and plenty of it is wrong.

What we built

Ask ten Vietnamese families how they hold a death anniversary and you get ten answers. In the Red River Delta many make the first offering the afternoon before; in the Mekong Delta plenty do it on the day itself. T y families invite a Then master, Khmer families go to the pagoda. All of these are real. Almost none of it is written down in one place. What exists online is mostly the same few pages copied and recopied, each copy a little different, none saying where it came from.

So instead of writing more articles, we built a structure first. Every rite in Nhat Nguyet is recorded the same way: its cycle and lunar date, where it s performed, who is honoured, which ethnic group and cultural region it belongs to, the order of the ceremony, the offerings, the taboos. Each of those fields carries its own source.

The sources come in layers. At the bottom are scholarly books, mostly public domain now: Phan Ke Binh s Vietnamese Customs from 1915, Nguyen Lien Phong s 1909 verse record of southern customs, Dao Duy Anh s 1938 cultural history, Toan Anh s work from the 1960s. On top of those, recent research by Ngo Duc Thinh, Tran Ngoc Them and Dinh Khac Thuan. Then heritage files: UNESCO nominations for the Giong Festival, Hung Kings worship and Then practice, plus ritual records from the Hoi An heritage centre. Press articles only count if they come from a list of 124 vetted sources.