World Clock is a fantastic native app that not only makes it easy to add all the time zones you care about and shows them on a map to better help you visualize the time differences, but helps you schedule meetings across time zones too.
Simple and powerful world clock:
• Add cities and timezones like GMT and UTC with a few key strokes.
• Convert international times with a drag of a cursor.
• Schedule international calls and meetings and add them to your calendar.
• Add Interactive Widget to your Notification Center
• Transform your desktop with an elegant World Clock screen saver.
• See weather at every location at a glance
Easily tell what time it is with clocks that change color with time of day:
— black for evening and night,
— white for morning, and
— green for working hours.
OS - MacOSX 10.7 or Later
Home Page - https://itunes.apple.com/us/app/id858446756