It isn't today, but we've built Bottlerocket in a way that it can be extended to work on bare metal or other places outside of AWS. There are a few issues on our github[1][2] that are similar that you're welcome to watch or contribute use cases to.
As far as running in non-AWS contexts, we haven't had time to head down that path yet, but as I mentioned in an earlier post, we've tried to build Bottlerocket in a way that it can be extended to work outside of AWS either as VMs or even bare metal. In fact, a few of the engineers on the team have been playing with getting it running on their RaspberryPi's at home :)
Answering your initial question and this one: Bottlerocket today only runs in EC2, but we've tried to make it flexible enough to run outside of a hypervisor on bare metal in the future (in fact, a few engineers on the team are really excited to get it running on their RaspberryPi's at home; toasters haven't been added to our roadmap yet ;) ).
Bottlerocket has a GNU userland like many other distros. It is just one that is stripped down of many things including removal of interpreters, shells, and package managers.
If you want to explore more deeply, you can enable the admin container and jump into a shell on the host[1] to look at the filesystem and see what Bottlerocket's userspace looks like up close and personal. You can also see a bit more of this debugging/exploration tooling explained in an AWS Partner Blog[2].
While our first variant is focused on Kubernetes and EKS, we have designed Bottlerocket in a way that new variants can be built that work with other orchestrators, or even without one (we have ECS support on our roadmap already). Also, we really enjoyed working in Rust for big chunks of this!
[1] https://github.com/bottlerocket-os/bottlerocket/issues/841 [2] https://github.com/bottlerocket-os/bottlerocket/issues/1097