It is my understanding that quasar gives you something awfully close to preemptive scheduling. It&#x27;s not quite as strict as Erlang&#x27;s reduction based appproach, but it essentially provides implicit cooperative scheduling. It allows you to do blocking IO without tying up execution.<p>On top of quasar, using Azul as the garbage collector will get you a GC without Stop-The-World behavior on the JVM. It&#x27;s neither open source nor cheap though.<p>That said, I&#x27;m plenty happy with BEAM.