CVS is a "version control system, and important component of Source Configuration Management (SCM)" Using CVS is quite easy once it is installed. It feels like a command line web grabbing or FTP grabbing program such as snarf, but uses a different protocol.
One problem can be that the version of a program obtained via CVS can be so cutting edge that it does not compiler and/or work. You normally find this out the hard way.
The present versions are quite easy to compile.
The version of GNU CVS used at the time of writing was CVS 1.10 (13th September 2000). This was compiled on an SGI O2 running IRIX 6.5.9.
"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."
Some FTP sites you can download the source code (presently 2.5 meg of tar.gz file)