Subversion "SVN" is a version control system, see http://subversion.apache.org/ and http://en.wikipedia.org/wiki/Subversion_(software)
Currently (2015-12) at version 1.9.2
See also: http://tortoisesvn.tigris.org - Subversion client
tkcvs as of version 8.0 now supports Subversion in addition to CVS.
BDK Has been working (albeit slowly) on a small package for parsing the dump file format produced by svnadmin dump. His ultimate goal is to use this to index a Subversion repository for the purpose of providing full-text search capabilities. Current code is at  should anyone care to take a look or use it.
CrowTDE has subversion integration in version 0.5.
RLH 2018-02-06 - Since you can use any language to make subversion hook scripts, I wonder if any Tcl'ers have done so and would share.