World Clock is a lightweight and intuitive app that allows you to check timezones, informations and various facts for every city in the world.
Just open the app, add your favourite cities and then you're done.
Do you want to display a widget on your home screen with all the timezones? You can do that as well.
Other than timezones, with World Clock you can check the local weather, curiosities, points of interests and a gallery of beaufitul photos of any city you like. Everything you need for planning your travel is right into one single app.