Expressive Languages for the JVM (JRuby/Mirah)

Thought you guys might enjoy "Expressive Languages for the JVM", a Google
Tech Talk by Charles Oliver Nutter, from Engine Yard.

The first half is on JRuby and talks about threading, JVM optimizations,
scaling Rails, had a couple demos, and gives a Ruboto demo (Jruby on
Android).

The second half talks about Mirah (the language formerly known as Duby). I
don't have experience with it, but it seems to be Java with Ruby based
syntax (I think they actually use Ruby's parser) and some added features.
But unlike JRuby, which requires you to load and run additional files, Mirah
compiles to pure Java / Bytecode, so you don't need to carry anything around
with you, like the JRuby runtime. In other words, you get Java performance
and portability, but ruby aesthetics, and some additions like closures,
mixins, and optional arguments. They also showed an Android app written in
Mirah, and a web framework for App Engine called dubious that is very very
strongly patterned after Rails.