This website is written in Hugo. Hugo is the static website engine behind the wonderful RStudio package blogdown, and is fast, popular, and easy to install and theme. See the Hugo docs for a quick orientation on how the site is organized. blogdown makes it easy to run Hugo from the RStudio editor and include R code in .Rmd content in Hugo sites.
To build and preview the site from RStudio, just use blogdown::serve_site(). blogdown::install_hugo() will get you set up the first time.
Hugo source files are located on the hugo branch of the codemeta.github.io repository (now the default branch on GitHub). So far we haven't set up automated builds, so deploying static sites on *.github.io repos is still a nuciance since the website must be on master branch. Building this repo will create and write the static site to ../website. I recommend setting the upstream origin of website to codemeta.github.io master branch (e.g. checkout the master branch and copy .git dir into website/ to deploy.)s