Blippy and Swipely both launched fairly recently with the hopes of making spending a social experience. Both services are very similar in that they both allow you to connect your bank and credit card info, as well as other accounts like iTunes and Amazon. After you've set everything up, as you start spending, you have the option to share these purchases with everyone. And now you can extend that sharing with the Blippy API.
Make no mistake, this service is definitely for the over sharers. While both Swipely and Blippy have had somewhat slow starts, both have proved themselves interesting enough, growing great user bases just itching to brag to their friends what they just purchased.
With Blippy and Swipely being so similar, it really comes down to who opens up first and it looks like Blippy has beaten Swipely to the API goldmine. By opening up their API, Blippy hopes that developers can take the the service to places and applications that we haven't quite figured out yet. Having an API like this is an incredibly important move for a new service taking on such a new niche.
Following the trend to kill off basic authentication, the Blippy API is "oauth and oauth only", a great choice for security reasons. After you've leaped the authentication hurdle, you can easily go to town making calls through the RESTful API.
Developers have a great deal of access to Blippy data, including individual purchase items, basic user data, products, and even friendships. This level of access really opens up what can be done. From a full-fledged Blippy mobile app to integration with existing applications. Blippy has also injected their humor into the API, with the addition of a "Unicorn" API call (seriously), allowing you to "fetch a rainbow" or "Gets a human reaction to seeing a double rainbow (sometimes triple)"
Currently, some things that I'd like to see in the API are missing. For example, you can't submit a purchase to Blippy and you can't update user information. I expect this to change, as the Blippy developer team is working pretty rapidly to roll out new API calls.
Blippy's development team wants to remind developers that the API is still fairly new, but all in all, it's pretty rich. You can head on over to Blippy's developer page right now and get started with their API and documentation. There is also a Google group to help you along the way.