Here is a document class replacement for managing your library-style app based on Core Data. All the goodness of NSDocument / UIDocument with just the right functionalities when you don’t need to expose document-management functionality to your users.
Core Data now officially supports concurrency and I/O in background threads since OS X 10.7 and iOS 5. In the same release, Apple also brought the document architecture to iOS that leverages this new capability of Core Data. However OS X didn’t get the same level of multicore love. In this post, I’ll show you how to create a multi-core supporting document architecture application for OS X.