To start with the basics, these are all open-source Linux distributions. That means anyone -- yes, even you -- can take RHEL's source code and make your own RHEL-based distro. Mind you, that's much easier said than done.
You see, you can't simply pull the code from a Git repository and compile it. That would be way too easy. Instead, starting in 2011, Red Hat incorporated its own patches directly into its kernel tree. All the code's still in there, but, as one person put it at the time, "It's sort of like asking someone for a recipe for the family's chocolate chip cookies, and getting cookie batter instead."
Many, but not all. Indeed, RHEL doesn't even have a majority of the RHEL operating system family customer base. That's because if you just need an RHEL-style operating system for something simple such as web or office servers, you can easily find web and system administrators that can keep CentOS running without any outside help. The same is true for anyone not doing any fancy programming. There are lots of developers who know how to build software around the RHEL family.
Red Hat knows this. So, first, the company adopted CentOS in 2014. CentOS continued on its free license way, while Red Hat hoped it could persuade CentOS users to become RHEL customers. It didn't work out.
Nevertheless, Chris Wright, Red Hat's CTO, has said, "CentOS Stream is stable enough for production." Still, Wright added, "CentOS Stream now sits between the Fedora Project's operating system innovation and RHEL's production stability."
I take this to mean, CentOS Stream is stable enough for adventurous companies that value getting the newest features over a guarantee of rock-hard stability. Fedora, of course, remains Red Hat's community Linux for developers and users who want to be on the RHEL's family leading edge.
But, where does that leave the old CentOS users? For them, there are two major choices: AlmaLinux and Rocky Linux.
Remember when I said people were ticked off by Red Hat's CentOS Stream move? Two leading Linux developers, CloudLinux founder and CEO Igor Seletskiy, and CentOS founder and CIQ CEO Gregory Kurtzer, decided to respond by creating new RHEL clones. Both decided that the old CentOS needed to come back.
As Seletskiy said then, "The demise of the CentOS stable release left a very large gap in the Linux community, which prompted CloudLinux to step in and launch a CentOS alternative." CloudLinux, for those that don't know it, is a commercial RHEL clone, but it's designed especially for Linux web hosting.
AlmaLinux, however, is a free community Linux. Calling AlmaLinux's shots is the AlmaLinux OS Foundation. This is a 501C6 non-profit foundation.
Rocky Linux is also a free community Linux. It's governed by the Rocky Enterprise Software Foundation (RESF), a Type B Corp. The idea here, Kurtzer said, is that "Open-source projects should not be subject to corporate control or business agendas. What makes a successful open source project isn't having a single individual behind it or even having a massive company behind it; what makes it successful is having many individuals and many companies all supporting and managing it collectively, in line with shared interests. That has been our goal with Rocky Linux and the RESF from day one. The RESF charter and bylaws reflect our intent that neither Rocky Linux nor any RESF project will ever be controlled, purchased, or otherwise influenced by a single entity or individual."
Now both groups offer support for their RHEL clones, but you don't need to pay a penny to use them. As Kurtzer observed, "Support is the first offering in our open-source product lineup. We can do multiple support models, but the one that is most interesting and valued is 'by the person' rather than by the core, node, socket, or entitlement. In this model, we support the people by providing a level of escalation over and above what they might have access to now."
If you need serious corporate support, RHEL has a lot to offer. If your company is all about Oracle, you might as well use Oracle Linux.
Next, I'm not crazy about using CentOS Stream for production, but if you need the latest and greatest Linux features and you have in-house expertise, go for it. If you're a developer and you're happy with living with the bleeding edge, say hello to Fedora. Just please don't use it on production servers.
Finally, if you and your crew cut your teeth on the old CentOS, either AlmaLinux or Rocky Linux are excellent choices. Personally, I'm moving my servers from CentOS 7 to Rocky Linux 8.7, but you won't go far wrong with either one.