JSDoc is just an equivalent [1] to Javadoc [2] (and PHPDoc is another one). Those formats just describe what you can do with your comments in code that look like this:
/ * * some documentation * /
The Javadoc tool converts those comments to a collection of clunky HTML sites with documentation [3] that we all know.
What the project linked here does is similar: Just like the Javadoc tool, it converts your comments from code into a well-readable documentation -- but not with clunky HTML but in concise Markdown.
To see an example, just put this sample Java code [4] into the box and convert.
Works well, but how is this different from JSDOC[1]?
[1]: http://usejsdoc.org/