Red Hat Enterprise Linux (RHEL) is a popular commercial Linux distribution that is developed and maintained by Red Hat. While RHEL itself is not available for free, there are several options for free software that is based on or inspired by RHEL:
CentOS:
CentOS is a free, open-source Linux distribution that is based on RHEL. It is developed and maintained by the CentOS Project, a community-driven effort to provide a stable and reliable version of RHEL.
CentOS is intended to be a drop-in replacement for RHEL, and it includes most of the same software packages and features. It is available for free download from the CentOS website.
Fedora:
Fedora is a free, open-source Linux distribution that is developed and maintained by the Fedora Project, a community-driven effort sponsored by Red Hat.
Fedora is intended to be a testing ground for new technologies and features, and it is designed to be a leading-edge distribution that is at the forefront of free software development. It is available for free download from the Fedora website.
Scientific Linux:
Scientific Linux is a free, open-source Linux distribution that is based on RHEL. It is developed and maintained by Fermi National Accelerator Laboratory (Fermilab) and CERN (the European Organization for Nuclear Research).
Scientific Linux is intended to be a stable and reliable distribution for scientific and technical computing. It is available for free download from the Scientific Linux website.