From the documentation: The bookdown package is built on top of R Markdown (http://rmarkdown.rstudio.com), and inherits the simplicity of the Markdown syntax (you can learn the basics in five minutes; see Section 2.1), as well as the possibility of multiple types of output formats (PDF/HTML/Word/…).
Websites created from RBookdown
1. Warde Publishers / Dual Language project (Work in Progress!)