CentOS claims to be the "Community Enterprise Operating System". It is the most used and well supported rebuild of RedHatEnterpriseLinux, with updates to RHEL regularly appearing in CentOS with 24 hours.
Their website was apparently asked to tone down the mention that they are based on RedHat's work, so they claim only to base on the work of a "prominent North American Linux vendor". They however conform fully with the RedHat's redistribution policy, mainly changing packages only to remove branding and artwork, and aim to be 100% binary compatible.
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