A self-modifying esoteric language
\ (also known as backslash) is a self-modifying esoteric programming language where you are only allowed to use slashes and backslashes. Its original goal is to write a cheating quine.
This repo contains the original C++ interpreter of \ and its build distributions as Windows executables.
The specification of \ is very complicated because it's commands are complicated (Also, it is hard to convert from wiki formatting to Markdown), so I won't put it here, but you can see it in the esolang wiki.