vss2svn is a Perl script (vss2svn.pl) and accompanying C program (ssphys.exe) to migrate revision history from a Microsoft Visual SourceSafe (VSS) database to a Subversion repository. This combination of programs was designed by reverse-engineering the backend database structure of Microsoft's VSS repository. In doing so, the authors have made progress towards overcoming the inability of even Microsoft's own API to properly recover deep history from VSS. This also means that you don't actually need a copy of VSS or its libraries to convert your repository.
Subversion Labels is a set of scripts and server-side hook programs that allow people to give Subversion revision numbers more meaningful aliases (such as release-1.1.2beta), and use them instead of remembering revision numbers. It does not require modification/recompilation of the Subversion server/client code, and is aimed at people who dislike Subversion's tags-are-branches approach.
WANdisco's Subversion/CVS Access Control provides full authorization, authentication, access control, and audit capabilities that go well beyond what Subversion and CVS provide on their own. Administrators can implement and maintain the most complex security policies with a minimum of effort. Valuable intellectual property is protected and a complete audit trail is provided, insuring compliance with SOX and other regulatory requirements.