Yes, there's also akka which is being incorporated as scala standard lib, and F# MailboxProcessor. The thing is that erlang/OTP and its behaviors have many people pounding on heavily loaded apps in production and improving its toolchain, whereas GHC and akka have recently (last couple years I think) been working ot get the stack working: dispatchers and load balancing (like erland reds), and bring GC up to snuff

Akka looks pretty sweet, but it looks like you still have to worry about blocking code in external libraries. In Haskell (and Erlang, IIRC), blocking code is deferred to a background thread automatically so you don't have to be consciously on-guard for it. You also get proper pre-emptive multithreading, while Akka looks like a hybrid of an event loop and a thread pool.

Is this a substantial headache with Akka, in practice?

(late reply)

it's pretty hard to google akka deployments but:

http://www.quora.com/What-companies-are-using-Akka-commercia...

http://groups.google.com/group/akka-user/browse_thread/threa...

and in terms of memory overheads and how many erlang process-type things you can spin up:

http://akka.io/docs/akka/1.1/scala/tutorial-chat-server.html