Since Red Hat published its last one (9th) release (Red Hat Linux 9) in 2003, they decided not to provide free technical support & product certification any more, and fully turned to the development of Red Hat Enterprise Linux (RHEL for short). This made some Red Hat rebuilders (open-source Enterprise Editions, such as White Box Enterprise Linux, Tao Linux, X/OS Linux, Scientific Linux) were born at the right moment. The most active one is CentOS (short for Community Enterprise Operating System).