Rocky Linux is a community enterprise operating system designed to be 100% bug-for-bug compatible with Red Hat Enterprise Linux (RHEL) now that its downstream partner, CentOS, has shifted direction. Rocky Linux is led by Gregory Kurtzer, founder of the CentOS project.
Previously, the CentOS project was receiving patches and updates after (downstream) a new version of RHEL was released. They recently announced that they will now be shifting to an upstream build (testing patches and updates before they get included in RHEL). Rocky Linux aims to replace CentOS as they will function as a downstream build of RHEL.