Code Quality and Metrics have been a major missing piece in engineering process to the management to see the code level quality, trend it, measure it etc. We do have lots and lots of tools like PMD, Findbugs & CheckStyle etc to automate the code quality but no single view tool to manage them.
Sonar is one of the tool that integrates all possible metrics and tools and time based trending and so on. I tried my samples on the sonar, looks cool and it comes with a simple derby in-memory database for a quick trial.
We did something very similar to this internally, which we couldn't take it forward. Hoping this tool gets wider adoption in enterprises, i would defintely want to try this in my future projects.