Apache Subversion Version System (SVN) is an open source version control system. Access and revision to objects are carefully controlled, to prevent unauthorized access and alteration. Developers use SVN to maintain current and historical versions of files such as source code, web pages, and documentation.

Their Vision:

Subversion exists to be universally recognized and adopted as an open-source, centralized version control system characterized by its reliability as a safe haven for valuable data; the simplicity of its model and usage; and its ability to support the needs of a wide variety of users and projects, from individuals to large-scale enterprise operations.

Features:

Version support for all files and directories in repository, enabling administrator to track changes that have occurred and obtain earlier versions of files

Renamed/copied/moved/removed files retain full revision history

Free-form versioned metadata

Atomic commits

Merge tracking

File locking

Changelists to organize commits into commit groups

Preservation of file attributes, such as executable and read/write status

Apache network server support with WebDAV/DeltaV protocol

Write-through proxy using WebDAV

Interactive conflict resolution

Repository read-only mirroring

Parsable output, including XML log output

Full MIME support - users can view or change the MIME type of each file, with the software knowing which MIME types can have their differences from previous versions shown