The Instagram API PHP Class provides developers with easy access to the Instagram API's methods in PHP. This version of the library lacks a few important methods, but it can still perform user authorizations and help users access their basic information.
If you are building an image sharing service or a social network mashup, it's likely that you will want to incorporate face-tagging in your images. Maybe you'd like to go a step further and automatically detect faces in an image, similar to Apple's iPhoto. A Romanian developer has developed an API to help detect faces in images and return the box coordinates so that you can build any kind of app you want.
Windows Azure, the mobile back end as a service platform, has added custom APIs, Git, NPM, Android Push Notifications, along with a free SQL DB. As Scott Guthrie, who builds for Microsoft, demonstrates on his "Scottgu blog," the creation of custom APIs is extremely simple. Here's the first shot at the start of building an API that works with a to do list.