Everything curl is an extensive guide for all things curl.
The project, the command-line tool, the library, how everything started and how it came to be the useful tool it is today.
https://ec.haxx.se is the home of this book. It features accessible links to read the book online in a web version, or download a PDF version for offline reading. Unfortunately, the previously provided ebook formats are no longer provided by gitbook.com that we use to produce the book.
https://github.com/bagder/everything-curl hosts all the book content.