Developing mobile apps using ROR

There are two ways of deploying an mobile app. Do you want it running completely on the phone or can it be a web app disguised as an iphone/android app?

For the native app solution we can use the Rhodes.Rhodes is an open source Ruby-based framework to rapidly build native apps for all major smartphone operating systems (iPhone, Windows Mobile, RIM, Symbian and Android). These are true native device applications (NOT mobile web apps) which work with synchronized local data and take advantage of device capabilities such as GPS, PIM contacts and calendar, camera, native mapping, push, barcode, signature capture, and Bluetooth.

Rhodes is the ONLY framework with: support for Model View Controller (other frameworks force you to put all business logic into the view as JavaScript), synchronized data (the price of entry for enterprise apps), support for ALL devices (Android and iPhone is not “crossplatform”), and a hosted build service (RhoHub – which changes the game for mobile app development entirely). Rhodes has many other major advantages over every other framework and underlying SDK, which can be summarized as modern development goodness for mobile apps.

For the 2nd option, web app disguised as a mobile app, I'd recommend Sencha Touch. Sencha has done an amazing job mimicking the look and feel of native iphone/android apps with their Javascript library. With this solution it would be just like any other web app though it's targeted for android and iphone via it's UI.