As a note to myself, I found a reference to Cobertura this morning as I was reading through the CruiseControl mailing list. Cobertura is a tool to calculate the percentage of code accessed by tests (test coverage).
According to the FAQ, this is a fork of the jcoverage tool, with “prettier reports” and a more open development process.
As an aside, a developer from the project has also developed a PHP based reporting front end for CruiseControl. The developer states that the “ugly” source code can be found in his CVS repository in the web module.