[exabrial]

Vert.x is what you're looking for.

That being said, async/Callbacks tend to create a pile of spaghetti, with no measurable performance gain. It's certainly a style of doing things and it creates an odd abstraction that really doesn't mirror the way our [current] computers operate.

The benefit of "fibers" or "green threads" is they are less of a jump and doesn't involve rewriting everything.