Haven't noticed it being mentioned here yet: In the actor-concurrency vein, Clojure is vaguely like Elang, but targeting the JVM. Some comparisons vs. Erlang have been made. There was an interesting discussion relating to Clojure on the PLT Scheme list, starting with a message from Geoff Knauth. Benjamin L. Russell then observed that Clojure has no tail-call optimization — understandably since it