All I want is a static site generator that sits in an executable file in my project's directory and doesn't require any dependencies so that I can run `./ssg build` and have all of my Markdown files interpolated into my template files and put in their own directory. I don't want to have to install all of the dependencies for Ruby or Hugo or Blades, cool as this project looks. Are there any SSGs that fill that niche?

(A Python executable would be fine since pretty much every Linux computer has Python, but I don't want to have to deal with pip).

That's pretty much what hugo[1] is. Download the .tar.gz and put the executable wherever you want.

[1] https://github.com/gohugoio/hugo