Looks like everyone is converging on the same idea these days :-)

You might be interested in my project then: https://github.com/virtkit-dev/virtkit (also inspired by smolvm and similar projects). Default kernel included, but can also boot a custom kernel if necessary.

I built it at work to replace years of accumulated tooling around complex multi-stage docker/docker-compose builds. The same workloads now run more securely, often faster, and with much less disk space. Also acts as a Gitlab executor to run CI jobs in microvms :-)

Obviously built with AI (this would otherwise have been a multi-year effort... and therefore not exist at all!) but I think the design is not bad.

Still beta and under-documented, but already quite usable.

Edit: it's not just a runtime, it also replaces docker build with its own native build engine — the build steps themselves run inside microVMs (not "docker inside a VM"). I haven't seen any other tool actually do that, that's quite fun ;-)