You could always just boot Linux in your browser, and then run ruby 
within that :-)

http://bellard.org/jslinux/
http://bellard.org/jslinux/tech.html

I don't know if the following project is live, but it claimed to be able 
to run JVM in Javascript, in which case you could run jruby within that:

http://ejohn.org/blog/running-java-in-javascript/

-- 
Posted via http://www.ruby-forum.com/.