Brainfuck
An eight-instruction esoteric programming language created by Urban Müller. His goal was apparently to create a Turing-complete language with the smallest compiler ever, for the Amiga OS 2.0. He eventually reduced his compiler to under 200 bytes.
A Brainfuck program has a pointer that moves within an array of 30000 bytes, initially all set to zero. The pointer initially points to the beginning of this array. The language has eight commands, each of which is represented as a single character, and which can be expressed in terms of C as follows:
> ==> ++p;
< ==> --p;
+ ==> ++*p;
- ==> --*p;
. ==> putchar(*p);
, ==> *p = getchar();
[ ==> while (*p) {
] ==> }