What devices does it need, and must everyone be online?

A browser is enough: a computer or laptop for staff, and an ordinary phone for teachers and parents. There is no app to install from a store, no program that updates itself, and no special hardware to buy.

An internet connection is needed to open a screen and to save — including when a teacher marks attendance in class. That is why attendance is kept light: one screen, one roster, one save. The parent and teacher portals can also be added to a phone's home screen so they open like an app.