RubyMotion allows developers to use Ruby to write iOS and OS X applications. It uses an LLVM-based static compiler to compile apps down to machine code.
With the next major version, RubyMotion looks to take on Xamarin in the cross platform game. Due later this year, RubyMotion 3.0 will add support for the Android platform.
Ruby is, in my opinion, a more pleasant language than either Java or Objective-C. However, that in itself was not a good enough reason for me to pick it over Objective-C for my iOS work. Would I use it for Android apps? They promise that performance should not be an issue. RubyMotion compiles down to machine code on Android too. The ability to share code between platforms makes it somewhat more attractive, but it also brings up comparison with the more mature Xamarin stack. While Ruby is nice, Xamarin has C#, which is also a nice(er) language (than Java). And how about the ability to use F# in Xamarin? Functional programming is the new black isn’t it?
It looks like one thing will carry over from iOS and OS X to Android though: The eye-twitch inducing fact that ruby code favours liberal use of underscores while the Android framework, like Cocoa Touch, is firmly in the camel case camp.