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.
However, by looking at it and playing with a few simple examples, I think this is the one that looks the closest so far.
Definitely interested to see the FS support, and also some instruction on how to customize the images to e.g. pre-install common Python packages or Rust crates. As an example, I tried to use the MCP with some very typical use-cases for code-execution that OpenAI/Anthropic models would generate for data analysis, and they almost always include using numpy or a excel library, so you very quicly hit a wall here without the ability to include libraries.