HTML is the standard markup language used to create web pages, and its elements form the building blocks of all websites.

ReAdABLE Human Format is described as 'The ReAdABLE Human Format aims at Agile Documentation by making WRITING and READING document easier for End User and Developer alike, while allowing a high degree of flexibility' and is a Markup Language in the development category. There are six alternatives to ReAdABLE Human Format for Self-Hosted, Mac, Windows, Linux and Web-based. The best ReAdABLE Human Format alternative is HTML, which is both free and Open Source. Other great apps like ReAdABLE Human Format are MultiMarkdown, MEML, Textile and GitHub Flavored Markdown.
HTML is the standard markup language used to create web pages, and its elements form the building blocks of all websites.

MultiMarkdown, or MMD, is a tool to help turn minimally marked-up plain text into well formatted documents, including HTML, PDF (by way of LaTeX), OPML, or OpenDocument (specifically, Flat OpenDocument or ‘.
MEML is a Lisp-like markup language for web development that transpiles directly to HTML5. MEML has features like easier file imports, a developer environment tool (MLD), components that can be used on multiple pages, and more.
Textile is a lightweight markup language originally developed by Dean Allen and billed as a "humane web text generator". Textile converts its marked-up text input to valid, well-formed XHTML and also inserts character entity references for apostrophes, opening and...
GitHub uses "GitHub Flavored Markdown," or GFM, across the site--in issues, comments, and pull requests. It differs from standard Markdown (SM) in a few significant ways, and adds some additional functionality.
Texy! is a lightweight markup language as well as converter of this format to XHTML, in a form of a library written in the PHP scripting language. It allows the user to write structured documents without knowledge or using of HTML language.