From CentOS Project:
CentOS developers use Red Hat's source code to create a final product very similar to Red Hat Enterprise Linux. Red Hat's branding and logos are changed because Red Hat does not allow them to be redistributed. CentOS is an Enterprise-class Linux Distribution derived from sources freely provided to the public by a prominent North American Enterprise Linux vendor. CentOS conforms fully to the upstream vendors redistribution policy and aims to be 100% binary compatible. CentOS is developed by a small but growing team of core developers. In turn the core developers are supported by an active user community including system administrators, network administrators, enterprise users, managers, core Linux contributors, and Linux enthusiasts from around the world.
What's new in this version:
Version 6.4 has added Microsoft Hyper-V drivers, upgraded samba4 libraries, and deprecated matahari.