Markdown
Markdown is a lightweight markup language that can be used to add formatting elements to plain text documents. Created by John Gruber in 2004, it uses simple, readable syntax – such as # for headings, * for emphasis, and - for lists – that a parser converts into HTML or other output formats. It is widely used for README files, documentation, code comments, changelogs, and static site generators, precisely because it stays easy to read even before it is rendered. Several libraries implement Markdown parsing, such as league/commonmark, erusev/parsedown, and michelf/php-markdown.