CVS is a version control system, which allows you to keep old versions
of files (usually source code), keep a log of who, when, and why changes
occurred, etc., like RCS  or SCCS. Unlike the simpler systems, CVS
does not just operate on one file at a time or one directory at a time,
but operates on hierarchical collections of directories consisting of
version controlled files. CVS helps to manage releases and to control
the concurrent editing of source files among multiple authors. CVS
allows triggers to enable/log/control various operations and works well
over a wide area network (see man pages).