Version Control Systems

Version Control System (VCS) is a software that allows to manage changes of documents, programs, images and other information that is stored in form of computer files.

Some popular Version Control Systems:
■Subversion - cross-platform open source VCS with great User Interface implementations (TortoiseSVN is the most known implementation for Windows shell integration).
■Git - open-source VCS for distributed development that does not require a central server, yet lacks a convenient UI.
■Mercurial - yet another distributed open source version control system which is less popular than Git (5 times less popular, if you trust Google).
■TFS - is a Microsoft product offering source control, data collection, reporting, and project tracking, and is intended for collaborative software development projects. It is available either as stand-alone software, or as the server side back end platform for Visual Studio Team System (VSTS).

Martin Fowler conducted the survey on 99 developers in his company ThoughtWorks and its the result
The results were this:

Tool	Best	OK	Problematic	Dangerous	No Opinion	Active Responses	Approval %
Subversion	20	72	6	1	0	99	93%
git	65	19	1	0	14	85	99%
Mercurial	33	27	2	0	36	62	97%
ClearCase	0	3	14	41	41	58	5%
TFS	0	0	32	22	44	54	0%
CVS	0	14	59	11	15	84	17%
Bazaar	1	13	3	0	80	17	82%
Perforce	1	26	16	1	54	44	61%
VSS	1	1	11	64	22	77	3%

Acknowledgement
My sincere thanks to my collegue Ahmed Galal who support me in this article
References:
http://martinfowler.com/bliki/VcsSurvey.html
http://abdullin.com/wiki/version-control-system-vcs.html
http://en.wikipedia.org/wiki/Team_Foundation_Server