It is my understanding that quasar gives you something awfully close to preemptive scheduling. It's not quite as strict as Erlang's reduction based appproach, b

It is my understanding that quasar gives you something awfully close to preemptive scheduling. It's not quite as strict as Erlang's reduction based appproach, but it essentially provides implicit cooperative scheduling. It allows you to do blocking IO without tying up execution. On top of quasar, using Azul as the garbage collector will get you a GC without Stop-The-World behavior on the JVM. It's neither open source nor cheap though. That said, I'm plenty happy with BEAM.