Reposurgeon enables risky operations that version-control systems
don't want to let you do, such as editing past comments and metadata
and removing commits. It works with any version control system that
can export and import git fast-import streams, including git, hg,
bzr, CVS, and RCS. It can also read Subversion dump files directly
and can thus be used to script production of very high-quality
conversions from Subversion to any supported DVCS.

Homepage:
http://www.catb.org/~esr/reposurgeon/
