Do you mean the template engine, or is there a different one? I'd never heard of it, and a nodejs template engine [1] is the best my Google-fu could find.

If that's it, Jade looks like a specific way to specify HTML documents, which is probably the biggest use-case for Markdown, but not the only one. It's important to also have a generic markup language for "documents" in general, not just HTML pages. For example, I spent most of the day today writing R code in an Rmarkdown document which allows my data analysis to be somewhat self-documenting. If I had to use an HTML-specific markup language, it wouldn't have worked real well, and I might as well have just used LaTex.

[1] https://github.com/visionmedia/jade

I had never heard of it until now, but now that I've seen Jade, it doesn't seem like a replacement for Markdown at all. I use MD to add semantics, formatting, and links to text. 99% of the Markdown documents on my computer will never be rendered as HTML.

Because Jade requires you to know how HTML works. Markdown (and WordPress.com) are made for people who want to focus on making their content, so they shouldn’t have to worry about that - the technology shouldn’t get in their way.

What is it?