"Subversion is a free/open-source version control system. That
is, Subversion manages files and directories over time. A tree of
files is placed into a central repository. The repository is much
like an ordinary file server, except that it remembers every change
ever made to your files and directories. This allows you to recover
older versions of your data, or examine the history of how your
data changed. In this regard, many people think of a version
control system as a sort of 'time machine...'"