Subversion "SVN" is a version control system, see http://subversion.tigris.org/ and http://en.wikipedia.org/wiki/Subversion_(software )
Currently (2007-01) at version 1.4.3
See also: http://tortoisesvn.tigris.org - Subversion client
tkcvs as of version 8.0 now supports Subversion in addition to CVS.