Jeremy Ashkenas has introduced [Literate CoffeeScript][1], having been inspired by Donald Knuth's early work on [Literate Programming][2].
According to Knuth, literate programming provides higher-quality programs, since it forces programmers to explicitly state the thoughts behind the program, making poorly thought-out design decisions more obvious. Knuth also claims that literate programming provides a first-rate documentation system, which is not an add-on, but is grown naturally in the process of exposition of one's thoughts during a program's creation. The resulting documentation allows authors to restart their own thought processes at any later time, and allows other programmers to understand the construction of the program more easily.
Literate Source Code takes Jeremy's idea ( of using John Gruber's [Markdown][3] for writing the documentation ) and applies it — without any restrictions — to any programming language with a little help from [Grunt][4].