"One project, in particular, really caught my eye. It's called Orto and is an implementation of the Java Virtual Machine (JVM) in JavaScript. This means that you can take an existing Java application, compile it to bytecode, run it through Orto (which produces the JavaScript, and embed it in a web page. While it doesn't provide the full capabilities of most Java code it does provide enough to make for some interesting demos." In a separate post he also detailed how the "HotRuby" project is allowing a Ruby VM to run in a browser using JavaScript or even indirectly using ActionScript in Flash.
http://ejohn.org/blog/running-java-in-javascript/
