Clojure is a general purpose language that targets the Java Virtual Machine, CLR and JavaScript. We briefly mentioned that it compiles to Java Byte Code. The ClojureCLR port which is written in C# enables it to target the CLR as well. Clojure is a dialect of Lisp which enables query language. It offers a transactional memory system and a reactive Agent system that ensures correct multithreaded designs. What sets Clojure apart is the immutable data and the first class functions. It helps to see Clojure language as a platform.
Features include
1) dynamic development - the Read Eval Print Loop (REPL) provides a console interface to try out Clojure commands. Clojure programs need not be compiled and run as in this case.
2) Functional Programming - fn and defn provide ways to define first class functions. Clojure provides a set of immutable lists, vectors, sets and maps where the older version is persisted and the newer versions are not a full copy.
3) Lisp Clojure is a dialect of Lisp for example 'and' is a macro
4) Runtime polymorphism 'proxy helps support implementation of interfaces
5) Concurrent programming shared objects are changed threadsafe with 'dosync', 'ref', 'set' and 'alter'. 'def' and 'binding' support isolating changing state within threads.
6) Hosted on the JVM - compiles to JVM bytecode and supports Java interfaces and classes using 'reify' and 'proxy'.
 Stackoverflow posts gives the following Clojure code for factorial:
(defn fact [x]
   (loop [n x f 1]
         ( if ( = n 1)
                  f
                  (recur (dec n) (* f n)))))