I have high hopes for Duby becoming a viable alternative to javac! Since it uses the native typesystem and doesn't require a runtime, it is 'just' a Ruby-like syntax for writing code for the JVM.
FWIW, Duby is not "done" or "ready" yet, but it's moving along. The promise of a static-typed language with all the expressive power of Ruby (or at least, Ruby's syntax), but the performance of Java and no runtime library is very compelling to me.
Is Duby really ready for production yet? The twitter posts referenced are blocked, but it appears at least someone is using it for production stuff. Anyone else?