Hey Product Hunt! Timezone Watch came out of a simple annoyance: I work with people across a few time zones and kept doing mental math to figure out if it was a reasonable time to message someone. Now I just glance at a row of clocks.
Each clock shows analog and digital time, day/night shading, and the UTC offset, and you save your own list of cities so it's ready every time you open it. Free web version installs like a native app and works offline once loaded — native builds for desktop, Android, and iOS are also on the site.