From the website: '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. Markdown is a very simple language but made powerful thanks to Pandoc, and bookdown has added a few important missing features related to writing books, such as figure/table caption numbering and cross-references, and embedding HTML widgets or Shiny apps. We have tried hard to make everything work for all output formats (PDF, HTML, and EPUB, etc), so your readers can choose their favorite file format to read. Although the bookdown package was developed using R, it does not mean your book have to be related to R at all. You can certainly write poems or novels with bookdown!"