ObjectiveResource: An Objective C port of ActiveResource puts the iPhone on Rails
ObjectiveResource (or Github repository) is a framework for iPhone developers (or, conversely, Rails developers who want to branch their app out to the iPhone) that allows you to interact easily between iPhone and Rails apps.
In essence, ObjectiveResource s a port of Rails' own ActiveResource - the library that enables RESTful communication of model data between apps. In this way, OR makes it easy to interface iPhone and Rails apps (or other apps that support an ActiveResource-esque protocol) in both directions.
There's a 6 minute screencast to bring you up to speed along with some brief Getting Started documentation. A sample application is provided that enables you to be up and running quickly, especially since it includes both an iPhone app and a Rails app.
If iPhone development is your bag, or if you're just curious, and you want to stay on top of iPhone developer news, check out MobileOrchard, a sister site of Rails Inside that focuses on the iPhone and iPod Touch development community.