These people people got up to 2M concurrent TCP connections
http://blog.whatsapp.com/index.php/2012/01/1-million-is-so-2...
And on top of it, it is using isolated heaps. That is beautiful I think. Completely concurrent GC is beautiful.
I know Erlang syntax is not to for everyone's taste (I do like it though). There is also Elixir (http://elixir-lang.org/). But the underlying BEAM VM is an awesome piece of technology.
> The thought was to have a billion threads on a SPARCStation 10
There are some green-thread C libraries I've been playing with, like Protothreads ( http://dunkels.com/adam/pt/index.html ) and libconcurrency ( https://code.google.com/p/libconcurrency/ ) I think they use setjump/longjump trick. Some use setcontext()/getcontext() POSIX call.
I still like Erlang VM best.