I’ve been kicking the tires on Sonar.
I’ve used code analyzers, Checkstyle, PMD, Findbugs, Cobertura, for a number of years, and looked at Sonar a while ago. But now revisiting it, Sonar seems to be the way to go to integrate all of these open source tools. Sonar is a Java-based web application that runs out of the box in a Jetty server with a Derby file-based data store. For industrial use you deploy it to Tomcat with a MySQL or Oracle database behind it. The UI is astounding! And the Nemo site is a showcase for Sonar.
The Nemo site is Sonar. You can browse through many open source projects there and see how it works without having to download or install anything. Sonar itself is included in the projects analyzed!