Click here to launch a new browser tab in which this tool will load, in all its glory.
It looks as though this tool uses IP address geolocation to discover your local time. Then it gives you a slider so you can move your target time around, to see who you have to wake up early or keep up late for your next international conference call.
Having done this in excel for several years now, this is a nifty upgrade! It's in Beta, so keep your eyes on this one. Apparently it works on iPad as well, so one may hope for an iPhone and/or Droid version of the applet as well.