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.