Appoint.ly. A simple appointment scheduler that synchronizes with your Google/iCal/Outlook Calendar so that your customers can check when you’re available and book a meeting. Once they schedule one, it's automatically placed in your calendar, so you don’t need to do anything except for sharing a link to your Appoint.ly by e-mail or on your website. Your customers don’t need to be logged in, they won’t see what other appointments you have and you can define many appointment types for different meeting durations (eg. 30-min, 15-min). And yes, it does have time zone synchronization, so it can be used to make appointments with people from all over the world. "No back-and-forth emails, no double booking and only a few seconds to schedule an appointment with you."