> I have not seen "befunge" as a euphemism for brainfuck before.  Is
> that common?

It's a different language, befunge is a 2d language.  Your text file is
like a grid.  IIRC, among the commands > < ^ v change direction right,
left, up and down, respectively.  So this would be an infinite loop:

>v
^<

The link was to an IRC bot, I think it runs in perl's Inline::Befunge
module, but I really don't know.  If you wanted to track it down, I'd
recommend asking at #esoteric on freenode.  Also, see this for more on
befunge http://esoteric.voxelperfect.net/wiki/Befunge

Hey, I don't know if there's a ruby interpreter for it!  Making
one would definitely be a fun evening with a beer.

Nor seemingly does there seem to be an interpreter in excel...
actually I think Excel would be great for this sort of thing, seeing as
it's a 2d grid.

You could have one part of the sheet containing the program
instructions, and have another part of the sheet contain the registers
(I think it uses registers?) and the 2-dimensional program counter.

The formula would just have to update the state based on the position
of the program counter and the instruction at that point.  Then it
would have to update the program counter...