RestKit is an open source Objective-C framework that simplifies interacting with RESTful web services for iOS apps.

It comes with a clean and easy-to-use HTTP request/response API with a powerful object mapping system that minimizes the amount of code to be written.

The framework provides integration with Apple’s Core Data framework which allows it to persist remotely loaded objects directly back into a local store, either as a fast local cache or a primary data store that is periodically synced with the cloud.

And, RestKit supports JSON via the SBJSON and YAJL parsers.

Fluidium, similar to Adobe AIR but open source, is a platform for developing Rich Internet Applications that run as native Mac OS X desktop apps.

Although there are many new applications that are built as web apps., native Cocoa applications still provide the best user experience on Mac OS X.

Fluidium can wrap your existing web app in a pure, native Mac application shell to provide the best of both worlds to your demanding user base.

It is based on the same open source technology that powers the popular Mac OS X Site Specific Browser: Fluid (which was discussed here).