TrueNTP

Clock face: turn your phone on its side and the corrected time fills the screen, with the date, the error bar, and how far your phone's own clock is off. The screen stays awake while it shows, so you can prop it up as a reference while you set another device's clock. No ads on the clock face. iPhone Duo: fully open, the time is shown much larger. Stand it half folded on a table and the clock sits on the upper half, with the time servers on the lower half. The clock face now says when a sync fails, instead of waiting quietly. Server details: long IPv6 addresses wrap instead of running off narrow screens, and the panel can grow past half the screen so pro users can reach the raw NTP fields and per-sample scatter.