The short answer is that Qi4j is a framework for domain centric application development, including evolved concepts from AOP, DI and DDD.

Qi4j is an implementation of Composite Oriented Programming, using the standard Java 5 platform, without the use of any pre-processors or new language elements. Everything you know from Java 5 still applies and you can leverage both your experience and toolkits to become more productive with Composite Oriented Programming today.