alan.ps, by Steve Hawley (hawley@mv.us.adobe.com), is a Turing Machine.

  MOST USEFUL -- 2nd prize
  -- The most useful, yet complex and twisted, program.

/it is the input text (obvious name, huh?).  It must start with an x, be
followed by a series of 1's then a series of twos.  Change the number
of 1's and 2's and watch the output to see what happens.
 
/tm is also input, but the correlation between tm and it is not obvious,
but when you understand it you will see that tm is also an obvious name
as well as the name of the program itself.