Our API directory now includes 71 eCommerce APIs. The newest is the PayAnywhere API. The most popular, in terms of mashups, is the Seatwave API. We list 8 Seatwave mashups. Below you'll find some more stats from the directory, including the entire list of eCommerce APIs.
This tutorial from the FINRA Technology website explains how even novice developers can create a basic REST service for evaluating whether a number is a prime or not. The service is built using automated computing service AWS Lambda, as well as AWS API Gateway and IAM for authentication.