When we built an app that scraped Facebook to find your real-life twin, it didn't resonate in North Korea, Western Sahara, Chad, the Central African Republic, Congo, Eritrea, Burkina Faso, Guinea, or Sierra Leone. In the world's remaining 189 countries and territories, it definitely did. And we reached them all with zero media budget.

Coke Zero's job was to convince people it really did taste like the original. Instead of asserting it, we dramatized the idea of a perfect double. We took the similarity inherent in the product and handed it to consumers: if Coke Zero is a lot like Coke, why not let people find someone who's a lot like them?

You logged in with Facebook and the app analyzed your photos the way a person sizes up a face, reading skin tone, bone structure and the angles of your features. It searched every willing participant, returned your closest look-alike with a match-accuracy score, and got sharper as more people joined. Then the fun part: it handed you a pre-written message so you could reach out to your double and say, we look alike, pretty crazy.

More than a million matches were made by 600,000 unique users, in over 189 countries, with no media cost after launch. New visitors converted at 91%, average time on site doubled versus the prior year, and within ten weeks people were tweeting about their doubles in a dozen languages. The press treated it as news, not advertising, from the New York Times and the Wall Street Journal to CNET, Fast Company and Mashable.