So did every other vendor. We have two CoreOSes, Flatcar, Container-Optimized OS from Google, Bottlerocket, k3OS, etc. Fortunately these aren't just different in name; there's a lot of experimentation going on around different ways to do updates, security, etc. I hope we'll eventually see some convergence after a few years.

Two CoreOSes? The one being Fedora CoreOS and the other..?

Fedora CoreOS and RHEL CoreOS.

Dead :)

You mean, the CoreOS that was end-of-lifed four months ago?

CoreOS lives on as Flatcar Container Linux. https://twitter.com/kelseyhightower/status/12831024012520980... It's a fully-compatible, drop-in replacement.

At least "Fedora CoreOS" still seems to be a thing.

And Red Hat Core OS (RHCOS) for Red Hat flavored shops.

Red Hat bought the company that created CoreOS so it's not surprising they have Red Hat/Fedora supported versions right?

Yep, very much agree. Container Linux was still very young and growing, but had some great promise. Incorporating the tech into RHEL and Fedora was a great idea IMHO. I think CoreOS was acquired for that specific purpose personally.

Not sure. To me Flatcar brings the original CoreOS spirit..

I'm not able to find concrete examples of the differences between Flatcar and Fedora CoreOS aside from FCOS using rpm-ostree.

What are the differences especially regarding their spirit and philosophy?

I don't think. Fedora CoreOS is more coupled to be an OpenShift node than a plain Container/K8s node. it's sad what they did. And I was a Fedora user for my whole life, but that made me reconsider.