OpenGrok maintains code version history. I am currently unsure of whether it looks at the CVS versioning information or whether it compares files between indexes. There is also options for many diffs and comparing different, non-concurrent versions.[http://cvs.opensolaris.org/source/history/on/usr/src/uts/sun/io/eri.c Example]  After a little looking at the OpenSolaris OpenGrok, it seems that the version histories are more Wiki style than CVS style, so they are arbitrary