We are using Fossil VCS.
http://fossil-scm.org/index.html/doc/trunk/www/index.wiki
Book - http://www.fossil-scm.org/schimpf-book/doc/tip/fossilbook.pdf
GUI for it http://code.google.com/p/fuel-scm/
It is simple, easy to use, one file without dependency, easy to move repository.
You can browse VCS at http://www.nex-hack.info/vcs/
Use following details for cloning or reading:
login - nex_dev , password - nex_dev
As fossil is just single file, all you need is download installation and clone repository
fossil clone http://name:password@nex-hack.info/vcs/fossil.cgi FwTool.fossil
Check book or site for further commands.
You need to send changes to Vitaliy_Kiselev or kenan for checking and push them into global repository.
DiffMerge is good free tool available for most OSes.
You can use it with any VCS.
Git is not the best choice for beginners and many developers do not like it much.
http://reprog.wordpress.com/2010/05/10/git-is-a-harrier-jump-jet-and-not-in-a-good-way/
http://reprog.wordpress.com/2010/05/12/still-hatin-on-git-now-with-added-actual-reasons/
Good book on distributed version control systems - http://www.ericsink.com/vcbe/vcbe_usletter_lo.pdf