Actors Guild is an experimental Java framework to make concurrent programming easier. It combines the concept of Actors with Futures. The result is a small API that let's you write concurrent, multi-threaded code almost like regular Java classes.

Example of a simple actor:

abstract class Counter extends Actor
{
    private int count;

    @Prop abstract int getInitialCount();

    @Initializer
    public void init() {
        count = getInitialCount();
    }

    @Message
    public AsyncResult<Integer> getCount() {
        return result(count);
    }

    @Message
    public AsyncResult<Void> add(int a) {
        count = count + a;
        return noResult();
    }   
}

Creating the actor and using its messages:

Agent agent = new DefaultAgent(); // the Agent manages Actors
Counter counter = agent.create(Counter.class, new Props("initialCount", 1));
counter.add(5).await();           // call add(), wait until message has been processed
System.out.println("Result: "+counter.getCount().get());  // will print 6

More information on Actorsguildframework.org.