There have been a couple of attempts.
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WebForth by FIG UK is a direct descendant of Mike Losh's earlier Java e-Forth and is still online at http://www.figuk.plus.com/webforth/En/Intro.htm. The WebForth site includes programming tutorials and Forth examples.
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http://www.mistybeach.com/products/Forth/ -- Embedding Forth in the JavaVirtualMachine, with the ability to call into the Java class libraries. Not fully baked, but quite promising. A pretty good environment for learning Forth and the class libraries, due to the stack and dictionary browsers. (Freeware, but not open source.)
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http://www.dataman.ro/dforth/ -- There is an old version of Delta Forth DotNet that compiles to JavaByteCode.
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http://leonardoce.interfree.it/leoforth/ -- LeoForth, which has some Java-related words (jnewn and jinvoken, for creating instances of java classes and invoking methods on java objects, respectively), and in which the stack is composed of java objects.
Should we make another page for ForthInJavaScript?
See JsForth and http://forthfreak.net/index.cgi?ForthInJavaScript.