Rubymetakoans is a project mainly written in RUBY and JAVASCRIPT, it's free.
Ruby metaprogramming koans online
Ruby Metaprogramming koans is hosted at: http://rubymetakoans.heroku.com. Use it to begin learning Ruby metaprogramming directly from the browser without having to install ruby, git.
Ruby Metaprogramming koans online is the browser version of Metaprogramming koans (https://github.com/sathish316/metaprogramming_koans)
If you're learning Ruby, checkout the original Ruby koans or the online version of the original Ruby koans from which this project is derived: