!!There are many version control systems.

* [CVS]
* Rational ClearCase
* [RCS]
* Perforce
* Microsoft Visual SourceSafe
* Subversion from [tigris.org|http://subversion.tigris.org/]
!!Visions, comments:

Does anyone know if there is such VCS that supports simultaneous editing of file, so that both editors can see each others cursor/caret moving and editing things.\\Any comments why this would /wouldn't work. --[tuomasp]

I suspect this would be more the field of editors, collaborative tools, shared whiteboards, conference software, and the like. Never heard of a vcs 
integrating that. Not a bad idea, as such. Anyone up to coding an emacs
mode for this? =)  --[ebu]

!Comments about ClearCase vs. CVS:\\
CVS roxx, ClearCase suxx =). Seriously, I have used a little bit of both, and from the developers/users view CVS seems much more easier to use. ClearCase (at least the installation I have used) has problems with who owns which branch, especially when project is proceeding between phases. --[tuomasp]

Yes, I've really learned to dislike ClearCase during my seemingly endless project at this large Finnish rubber boot manufacturer. To Windows client is especially bad and buggy, very prone to crashes and slow to boot. So I'm pretty much using the commandline utility (cleartool) to do all my operations to CC.

Also, CC seems the get pretty easily confused about different versions and views, so every now and then you'll get a merge error and have to manually merge the files. I've also encountered lots and lots of files that show up as either hijacked or checked out on my machine, while in reality they are just fine and checked in. Go figure.

The good thing about CC is its good integration with other Rational's software products like Rational Rose. I even found a plugin that allowed [NetBeans]to use it directly from its project/filesystem tree.

Oh, and there's another version control system called SubVersion, which I think is based on CVS. It adds one sorely missed feature to it, the ability to move/rename files and directories.