mdBook is a command line tool and Rust library to create books using Markdown. It's very similar to Gitbook but written in Rust.
This book serves as an example of the output of mdBook and as the docs at the same time.
mdBook is free and open source, you can find the source code on Github. Issues and feature requests can be posted on the Github Issue tracker.
mdBook, all the code and this book, are released under the Mozilla Public License v2.0