Antora is described as 'A static site generator for creating documentation sites from AsciiDoc content aggregated from multiple repositories. Made by the creators of Asciidoctor' and is a Documentation Generator in the Development category. There are more than 25 alternatives to Antora for a variety of platforms, including Self-Hosted solutions, Linux, Mac, Windows and Python. Most alternatives are Documentation and Static Site Generators. The best alternative is GitBook, which is free. Other great apps like Antora are Read The Docs (Free, Open Source), MkDocs (Free, Open Source), Sphinx (Free, Open Source) and Daux.io (Free, Open Source).
Read the Docs hosts documentation for the open source community. It supports Sphinx docs written with reStructuredText, and can pull from your Subversion, Bazaar, Git, and Mercurial repositories. The code is open source, and available on github.
Daux.io is a documentation generator that uses a simple folder structure and Markdown files to create custom documentation on the fly. It helps you create great looking documentation in a developer friendly way.
docsify generates your documentation website on the fly. Unlike GitBook, it does not generate static html files. Instead, it smartly loads and parses your Markdown files and displays them as website. All you need to do is create an index.
A documentation generator that builds HTML output based on Markdown files. Supports Markdown specs and offers a wide set of custom components using Markdown-like syntax. Builds Reference Source documentation for .NET projects (more added soon).