LibCVS Perl simplifies the job of writing tools around CVS by providing Perl libraries that programmers can access directly in their code. Its current focus is libraries that use the cvsclient protocol to talk to a CVS server and are targetted at the development of client applications. Libraries that understand the RCS file format and provide fast server-side access are a future possibility.
HO-CVS is a version control system based on MetaCVS. In addition to the features of MetaCVS, it features module level versioning, the ability to reference every version (since there is a tag after every commit, which is extremely useful but slow), complex versions like #v1.2.3 designed to carry information about the change, operation hooks, and a somewhat powerful log command.