Version Control Systems
Revision control, also known as version control or source control (and an aspect of software configuration management or SCM), is the management of changes to documents, programs, and other information stored as computer files.
CVS
CVS is the grandfather of revision control systems.
SVN (Subversion)
http://warren.chinalle.com/2011/09/20/svn-subversion/
Git
http://warren.chinalle.com/2011/09/17/git-vcs/
Mercurial
http://warren.chinalle.com/2011/09/10/mercurial-vcs/
Links
7 Version Control Systems Reviewed
http://www.smashingmagazine.com/2008/09/18/the-top-7-open-source-version-control-systems/
Intro to Distributed Version Control (Illustrated)
http://betterexplained.com/articles/intro-to-distributed-version-control-illustrated/
Comparison of revision control software
http://en.wikipedia.org/wiki/Comparison_of_revision_control_software