The key to any transaction whether in the online or physical world is the payment process. Payment is a common feature across desktop, web and mobile applications. PayPal is often the first choice that springs up on developers when they think of integrating payment into their applications. Developers want an easy to use API, sandbox testing, fair transaction fees and definitely less paperwork and wait time. Stripe aims to simplify the process of accepting payments on the Web with its easy-to-use Stripe API.
Our API directory now includes 180 finance APIs. The newest is the TTAGG Stock API. The most popular, in terms of mashups, is the PayPal API. We list 33 PayPal mashups. Below you'll find some more stats from the directory, including the entire list of finance APIs.