QWOP is an esolang by User:Rdococ. As the name suggests, it uses four characters: Q, W, O and P. All others are ignored.
Q is a quine. Here is the shortest non-null quine:
W is a conditional. If the input character is not equal to the next character, it will skip the next command:
O is a loop. It will return the pointer to the last O, if one exists. Here is an infinite loop:
P is a print command. It will print the next character rather than executing it: