The obvious alternative would be Ubuntu. The LTS releases are alternatives to RHEL/CentOS. The others are Fedora alternatives.
However, Red Hat is _far_ more than RHEL. They actually build a ton of OSS that's used in RHEL and elsewhere. Ubuntu does little more than repackage Debian. That's not a criticism. They package well, and they know how to polish. But there's no replacement for Red Hat as a company.