mdBook is a command line tool and Rust crate to create books using Markdown files. It's very similar to Gitbook but written in Rust.
What you are reading serves as an example of the output of mdBook and at the same time as a high-level documentation.
Alongside this book you can also read the API docs generated by Rustdoc if you would like to use mdBook as a crate or write a new renderer and need a more low-level overview.
mdBook, all the source code, is released under the Mozilla Public License v2.0