Brainf
Brainf*** (yes, it's a swear word, one that I never use) is an extremely simple programming language that is more a diversion than a practical language. Since it's Turing Complete (offsite), however, you can accomplish any computational task using brainf.The language consists of only 8 instructions ("<", ">", "+", "-", "[" ,"]", ".", ","). Even writing a typical "hello world" will bend your brain.
Here are some brainf resources (beware that these external link will contain profanity in the form of the language's name):
