GrassMudMonkey is a project mainly written in JavaScript, it's free.
an Open Souce GrassMudHorse/Whitespace Engine Written in JavaScript
GrassMudMonkey is a pure JavaScript implementation for GrassMudHorse programming language based on stack & heap. The only tokens used are '草','泥','马', other chars are ignored as comments.
http://www.limboy.com/demo/gmm/demo.html
GrassMudHorse homepage: http://code.google.com/p/grass-mud-horse/ Whitespace homepage: http://compsoc.dur.ac.uk/whitespace/