From the OpenGrok internals: To get the version control history Analyzer Guru, calls his old friend the good old History Guru. This guy is much older than Analyzer Guru, and his silky long beard almost touches the ground. He has several assistants called History Readers. They just read the version control log history for a given file and directory.

To add support for a new SCM system you need to implement your own Repository and add it to the list of known repositories in the RepositoryFactory.