ohShopify.php is a lightweight client that enables PHP applications to interact with the Shopify API. The client requires PHP version 4 with cURL support for its use. The client is compatible with OAuth Shopify Apps, and with valid authorization is able to access Shopify admin functionalities via Shopify API calls. This library is not officially supported by Shopify, but is endorsed on the Shopify API developer documentation list of 3rd party libraries. The package is maintained by Colin McDonald and is open sourced on GitHub.
MyBantu is an interesting little mashup, available as an iPhone app, an Android app, and a website. Its goal is to make shopping for anything, especially restaurants and movies, easier and more social. It uses Yelp API, Netflix API and various others to make it happen. It's very similar in idea to Siri, the "ultimate mashup" that Apple later gobbled up in the largest mashup acquisition ever.