I just remembered I made this thing for turning the Clojure code blocks in Markdown & AsciiDoc documents interactive a couple of years ago: https://github.com/eerohele/useless As per the name, I don't know that it's particularly useful, but it was fun (and educational) to make.

That's interesting @flowthing - and reminded me of a thing I made to convert Clojure code blocks in Markdown & AsciiDoc to tests: https://github.com/lread/test-doc-blocks