Bookdown is described as 'The bookdown package is a free and open-source R package built on top of R Markdown to make it really easy to write books and long-form articles/reports' and is an app in the News & Books category. There are five alternatives to Bookdown for Self-Hosted solutions, Mac, Windows, Linux and Online / Web-based. The best alternative is GitBook, which is free. Other great apps like Bookdown are Leanpub (Freemium), mdBook (Free, Open Source), Retype (Free) and Archivy (Free, Open Source).
GitBook is a tool for building beautiful books using Git and Markdown. It can generate your book into multiple formats: Static Website: This is the default format, it generates a complete interactive static website.
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).