NixOS
NixOS is an independently developed GNU/Linux distribution that aims to improve the state of the art in system configuration management. In NixOS, the entire operating system, including the kernel, applications, system packages and configuration files, are built by the Nix package manager.
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CentOS
CentOS as a group is a community of open source contributors and users which started in 2003 and has been sponsored by Red Hat since 2014. CentOS Linux versions up to CentOS Linux 8 are 100% compatible rebuilds of Red Hat Enterprise Linux, in full compliance with Red Hat's redistribution requirements.