Tangler is a literate programming tool whose input format is HTML.
Read all about it at https://hober.github.io/tangler/
To extract Tangler’s source code from the HTML file, you can simply download the source files, or you can check out this repository and extract the Makefile with the following command:
node - index.html Makefile < bootstrap/tangle.js > Makefile
After this, a simple make should do the right thing.