Clojure is a new, dynamic programming language that is built upon the rock-solid foundation of the Java Virtual Machine, the industry-standard platform that is the foundation for Java, one of the world's most popular and powerful multi-platform languages. But, why write in Clojure if you want to target the JVM instead of Java? Wouldn't it make more sense to write your project in the language for which the virtual machine was designed?
Enter functional programming at its finest; Clojure doesn't just target the JVM. No, it's much more than that -- it's an implementation of Lisp. It's not your standard Common Lisp, however; it's a highly specialized form of the language. It's designed with everything modern functional programmers have in mind: concurrency, immutability, and perhaps most importantly, portability. That's right: all your current Java classes are compatible with Clojure.
Clojure doesn't stop there. The core data structures are immutable and extensible. Code-as-data has been extended to maps and vectors. Practically everything is abstract. Multimethods foster polymorphic programming. It really is an amazing thing.
To see what I mean, you should really have a look for yourself over at Clojure's website. The MIL already has a project that is built upon Clojure, CLIFF, which uses an embedded version of the language to generate forensics models dynamically.
As a functional programmer, writing in Clojure has been a dream come true. Do yourself a favor and hack something up today. :D