The Flickr Ruby library by Maël Clérambault aims simplicity of API access. What it does is to map the methods of the official API docs. At the same time, it returns methods intuitively. This library is always updated because of the introspective features of the new methods added continuously by flickr.
It's been a quick transition from app provider to API provider for photo-sharing Instagram and its Instagram API. Today the company launched a new Instagram Real-time API, which provides access to the site's content via webhooks as photos are added that match pre-determined criteria.