I created a world clock / time zone converter at itime.io because i felt existing solutions were too limited and not easy to use.
Main features are:
you can enter a date / time in any format
easily add as many cities as you want
saves the selected time zones in local storage so you don’t need to re-add the time zones next time you visit the page.
Here’s a quick animated gif to show the features.
Please check it out and let me know what you think!