Cult of the Bound Variable Universal Machine implemented in javascript http://www.boundvariable.org/task.shtml Note: for this to work from a local filesystem, you will need to start Chrome with the command line option "--allow-file-access-from-files" and put the sandmark.umz and codex.um files into the same directory as um.{js,html} . The codex.um file is obtained by running the codex.umz file in a UM interpreter; probably not this one, since it is too slow.