I think Racket is underrated. (Dunno about "most underrated".) It's a batteries-included Scheme/Lisp dialect with the best documentation I've ever seen, a stat

I think Racket is underrated. (Dunno about "most underrated".) It's a batteries-included Scheme/Lisp dialect with the best documentation I've ever seen, a state-of-the-art macro system, and a very friendly community. It has performance better than your typical dynamic language (Python, Ruby) though not as good as the highly optimized ones (Javascript V8, LuaJIT).