If you think that one-handed watches are useless, you obviously haven't seen the KUU Watch. The KUU Watch is a concept watch from designer Löytö Esineiden that tells time using one hand.
The KUU Watch has a rotating disk on its face used to tell the minutes of the hour. A needle on the disc points directly to both the hour and minute. The whole thing may sounds confusing, but it is actually pretty easy to read once you get the hang of it. I'm sold.