Apache Subversion:

In software development, Apache Subversion (formerly called Subversion, command name svn) is a revision control system founded and sponsored in 2000 by CollabNet Inc. Developers use Subversion to maintain current and historical versions of files such as source code, web pages, and documentation. Its goal is to be a mostly-compatible successor to the widely used Concurrent Versions System (CVS).
Features:
• Commits as true atomic operations (interrupted commit operations would otherwise cause repository inconsistency or corruption).
• Renamed/copied/moved/removed files retain full revision history.
• The system maintains versioning for directories, renames, and file metadata (but not for timestamps). Users can move and/or copy entire directory-trees very quickly, while retaining full revision history.
• Versioning of symbolic links.
• Native support for binary files, with space-efficient binary-diff storage.
• Apache HTTP Server as network server, WebDAV/Delta-V for protocol. There is also an independent server process called svnserve that uses a custom protocol over TCP/IP.
• Branching and tagging as cheap operations, independent of file size (though Subversion itself does not distinguish between a tag, a branch, and a directory)
• Natively client–server, layered library design.
• Client/server protocol sends diffs in both directions.
• Costs proportional to change size, not to data size.
• Parsable output, including XML log output.
• Open source licensed — Apache License in the projected 1.7 release; prior versions use a derivative of the Apache Software License, v1.1
• Internationalized program messages.
• File locking for unmergeable files ("reserved checkouts").
• Path-based authorization.
• Language bindings for C#, PHP, Python, Perl, and Java.
• 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.