Svn server is a subversion server. Subversion is a powerful tool for administration of file versions during programming or shared file modifications. Subversion is an alternative program for CVS. It is platform independent: so you can use it under Linux and Windows. I like most the capability to access the same working file from different operating systems. No need to bother about Windows or Linux working file formats: Simply work with your system and with the same working copy.
Svn server is mostly used by programmers (including hobby prgrammers!) who want to develop their code in a comfortable way.