JD | Java Decompiler Yet another java decompiler. But jad has been getting long in the tooth and has issues with newer java versions, and the author of the blog I just read was a jad user who jumped over. Possibly worth looking at the next time I decompile something. Both standalone and eclipse plugin versions.
Kato Looks pretty raw right now, but Kato is an apache implementation of JSR 326 - generation and consumption of post mortem and snapshot java diagniostics.
Java Simon API Simon is a monitoring api for Java that adds things like stopwatches and counters. It enableable via config and can do things like conditional logging of just the slow events.
Gatling Gatling is a web load test framework built in scala that attempts to address issues like "we don't have enough Load runner licenses" and "Jmeter doesn't scale" or "opps we modified the page and all the tests fail"
Naked Objects - Welcome to Naked Objects Interesting POJO framework. You only develop the business objects. Persistence is auto generated vi Hibernate (no shock), and the View and Controller layers are autogenerated as what they call an "object oriented UI". I probably wouldn't do this for a real app. Certainly not a customer facing app or even a non-trivial backend app. But for rapid prototyping the buisness layer DDDish, it might be a useful accelerant.
google-guice - Google Code Guice is Google's dependency injection framework for Java. As contrast to Spring, it's just dependency injection without all the other bulk that comes with Spring.