The various derivatives of Brainfuck are all joke languages. That said, Brainfuck originally had an at least interesting purpose: The idea was to create a lang

The various derivatives of Brainfuck are all joke languages. That said, Brainfuck originally had an at least interesting purpose: The idea was to create a language that could be handled by the smallest possible compiler. AFAIK a Brainfuck compiler can be implemented in less code than a compiler for any other Turing-complete language. Still not practical, but interesting nonetheless.