Disclosure – I’m the vert.x guy 🙂
Vert.x is a fully fledged platform for building polyglot, scalable, asynchronous web-enabled applications.
It is heavily inspired from node.js but goes further than node.js and provides a distributed event bus which reaches from the server right into client side JavaScript thus creating a super simple model for so-called “real-time’ web applications. We also ship with a mailer and a mongodb persistor. There’s a full tutorial here http://vertx.io/tutorials.html
But the probably the main thing that sets it apart from other async frameworks is it’s polyglot nature. The same (or similar) API is available in Java, Ruby, JavaScript and Groovy (with Clojure, Python and Scala support to follow).
Vert.x really takes advantage of true multi-threading on the JVM to provide scalability and performance than node.js cannot touch.
If you don’t want the whole platform. Vert.x can also be used as a library for providing HTTP, TCP, websockets, sockjs, eventbus, etc support in your Java or Groovy application.
For more info pls see the website http://vertx.io