Immutable data structures. Scala and Clojure both provide higher level facilities for concurrency then Java, Python or Ruby. Scala and Clojure both have solut

Immutable data structures. Scala and Clojure both provide higher level facilities for concurrency then Java, Python or Ruby. Scala and Clojure both have solutions for the expression problem, a very real issue when growing code bases (every OO language should have this) Clojure provides metadata - a lovely concept of attaching information to an object w/o affecting it's value or needing to 'wrap' it in a class. All these things add up to a significantly more productive experience. Especially as a project evolves over time.