Over at Instructables, SelkeyMoonbeam has figured out a clever way to make one analog clock tell the time of 24 different time zones. All you have to do is turn the clock's base to the city (or time zone) you're in, and the clock will show the right time.
It doesn't include the minute hand because the time would be off every time you rotate it but it does give you the correct hour for time zones all across the world. Think of it more like a gauge than an atomic clock, I guess. Here's how SelkeyMoonbeam, the maker of the clock, explains it:
It's not really that useful if you're a world traveler- you have to take the minute hand off or it's wrong every time you turn it. But the hours are right, so it's good for if you're doing international business, or have friends overseas that you want to contact. Actually, I was considering making a version that left off the cities and simply displayed the names of my wide-spread family members so that we'd have an easier time discussing when to Skype call.
The instructions on how to build one yourself are over at Instructables. [Instructables]