Git is a free, open-source distributed version control system built to handle everything from small scripts to very large codebases, quickly and efficiently. It's easier to learn than the alternatives of the time (Subversion, CVS, Perforce, ClearCase), and its cheap local branching and staging areas make day-to-day work faster.
Installing it on CentOS is a two-step process: add the EPEL repository, then install the package.
# Add the EPEL repository (32-bit CentOS 5.5)
rpm -Uvh http://dl.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm
# Add the EPEL repository (64-bit CentOS 5.5)
rpm -Uvh http://dl.fedoraproject.org/pub/epel/5/x86_64/epel-release-5-4.noarch.rpm
# Then install
yum update
yum install git git-daemon
That's it.