Cloud Hypervisor and Firecracker both have an excellent reputation for ultra lightweight VM's. Both are usable in the very popular Kata Containers project (as well as other upstart VM's Dragonball, & StratoVirt). In us by for example the CNCF Confidential Containers https://github.com/kata-containers/kata-containers/blob/main... https://confidentialcontainers.org/
There's also smaller efforts such as firecracker-containerd or Virtink, both which bring OCI powered microvms into a Docker like position (easy to slot into Kubernetes), via Firecracker and Cloud Hypervisor respectively. https://github.com/smartxworks/virtink https://github.com/firecracker-microvm/firecracker-container...
Poking around under the hood, microsandbox appears to use krun. There is krunvm for OCI support (includes MacOS/arm64 support!). https://github.com/containers/krunvm https://github.com/slp/krun
The orientation as a safe sandbox for AI / MCP tools is a very nicely packaged looking experience, and very well marketred. Congratulations! I'm still not sure why this warrants being it's own project.
I've thought about making one of these for other coding agents. It's not quite as trivial as it looks and I know how to do it, also on Windows, although it seems quite a few coding agents just pretend Windows doesn't exist unfortunately.