One day when I was supposed to be studying for a test I wrote this little interpretor for a minimalist language I made up. The language is so simple the interpretor is only 33 lines of perl. I named it ‘rat’ because that was the first thing to pop into my head and naming this thing didn't merit any more thought. You can try it out by getting this program which implements Euclid's algorithm for the gcd and this this one that uses it. Run it like so:

cat test.rat | perl rat

It ought to be more or less Turing complete, but it's pretty useless since the interpretor doesn't let you do much more than print out results as numbers. Also, trying to express an algorithm in this language is monstrously awkward.