From markdown.sile’s documentation.

With Djot and Markdown being made first-class citizens in SILE, you can now write your documents in these lightweight markup languages. … there is no need for you to delve into SILE’s default language or Lua programming. Yet, these options remain available under the hood for those seeking a blend of possibilities.

I keep forgetting the name of this app.

Everytime I wrestle with ConTeXt I’m like “this is the last time” but of course it never is because I have made so many templates that I want to keep using even as they keep breaking. But I’ve been looking for something for new projects and I’m leaning towards SILE over Typst or some of the CSS based options I’ve looked at (and also forgotten the name of). Not sure yet.