Maven plugin which includes build-time git repository information into an POJO / *.properties). Make your apps tell you which version exactly they were built from! Priceless in large distributed deployments... :-)
Revapi is an API analysis and change tracking tool written in Java. Its focus is mainly on Java language itself but it has been specifically designed to not be limited to just Java. API is much more than just java classes - also various configuration files, schemas, etc. can contribute to it and users can become reliant on them.