Clojure
Used by 11 peopleen.wikipedia.org ↗

“For more organized "systems", I've recently been looking at Clojure.”
Dorian Taylor Interview, Entropy schlepper, maker of toys and diversions · via Uses This 
“Then there's usually a clojure repl, and a test runner that automatically reloads and runs tests when I write files to disk.”
Kyle Kingsbury Interview, Computer safety researcher · via Uses This