[marviio]

I would bet it was written in orgmode.

[sokoloff]

Intro of the book confirms: “It is written in Org-mode, first made by Carsten Dominik and then developed by many other people. Diego Zamboni wrote the Org exporter to convert Org-mode syntax to Markua, expected by Leanpub.”

[codetrotter]

For anyone else curious about Markua: https://leanpub.com/markua/read