Rhomobile's Rhodes is one of the few cross platform frameworks for mobile applications. Besides using HTML/Javascript/CSS for the GUI part of applications, Ruby is the language to write Rhodes application logic.
The final version of Rhodes 2.0 is now available. The framework is now MIT licensed. Next to the features present in the Rhodes 2.0 Beta, the framework now also allows to use the platform's mapping components across all systems.
After Apple's change to the iOS SDK License Agreement, the future of many third party programming toolkits for the iPhone seemed in peril, particularly the ones shipping interpreters like Rhodes. The release notes of Rhodes 2.0 now show that Rhodes applications keep getting accepted to the AppStore:
And just an update for many of your because you asked but Rhodes apps are continuing to be accepted on the App Store (as we indicated they would be) even after the iPhone 4.0 Terms of Service went into effect. Some of the recent apps accepted include TrackR 2.0 (a free app for PivotalTracker), Metalingual (an app for language translation from Sarah Allen) and WorshipPlanner.
In addition, as announced a few months ago, there'll be ports of Rhomobile's sync libraries for at least Objective-C in a future release.
For more information on Rhodes see this InfoQ interview with Rhomobile's Adam Blum recorded at QCon London.
While Rhodes brings cross platform mobile development to Ruby using native versions of Ruby everywhere except on the Blackberry, there are some other efforts focused on getting JRuby onto Android. The Ruboto project brings JRuby to Android and Ruboto-IRB allows to develop JRuby scripts right on the Android device.
Ruboto was created by JRuby's Charles Nutter, and now a project in the Ruby Summer of Code, by Daniel Jackoway, is supposed to bring improved tooling for writing Android apps using JRuby later this year.