CVS is a version control system. Using it, you can record the history of
your source files. This means that it stores all changes made by one or
more developers to one or more source files.
Since version 1.10b CVS has KeyAgent support. Which gets used to login with SSH-keys, which is more secure.
For more information about CVS itself and what it does, please have a
look at the documentation on the official CVS website at one of the
following locations:
http://www.cvshome.org/docs
http://www.cvshome.org/docs/manual