Mark Watson lines them up...
Gambit-C Scheme does have the Termite package for concurrency but something more main-stream like Scala or Haskell seemed like a better idea.Ouch. Maybe lisp won't be our overlord.
Actually Gambit does not support multiple cores in one OS process either. It has Erlang-levels for threading, and almost as good for mailboxing, but just on one CPU.
So then Clojure? Good bit simpler than Scala or Haskell. Much more expressive for symbolic programming as well.
Mark points to an impressive comparison favoring Haskell over Scala. (Assuming all things being equal.) I wonder what the learning curve is to get really good numbers for various kinds of programs in Haskell, with its laziness, etc. Especially good memory usage numbers.