Yes, it's a [tag:popularity-contest]. Please read the entire question before downvoting or close-voting. The three headers make up the spec, and the bullet points below them make up the rules.
Your challenge is to design a [one instruction set computer][1] (OISC):
An [OISC] is an abstract machine that uses only one instruction – obviating the need for a machine language opcode. With a judicious choice for the single instruction and given infinite resources, an OISC is capable of being a universal computer in the same manner as traditional computers that have multiple instructions.
For the purposes of this challenge, an OISC is a [Turing-complete][2] programming language with a single command that takes at least one argument. It must take at least one argument to prevent it from being a [ZISC][5] or a [Lenguage][6]-equivalent.. You may take as many arguments as you want, as long as rule #1 is followed.