Popcarte is a service for consumers, taking their uploaded photo and turning it into a card of the customer's choosing, from postcards to invitations to thank you notes, to special occasions, and then mails it out worldwide. The Popcarte API lets developers integrate the service into their apps.
There is nothing more satisfying than sharing that once in a lifetime shot with the world, except maybe seeing that it has been viewed by a few thousand people. These kinds of stats have been collected by Flickr for quite some time, and now they are available to developers thanks to some new functions added to the Flickr API.
The most popular API, in terms of mashup count, is far and away the Google Maps API, which accounts for 41% of all mashups. But when it comes to the most popular pair of APIs, Flickr and YouTube mashups are the most common. Not to be outdone, Google Maps joins Flickr in a near second place.