You can handroll a lot with: https://github.com/nestybox/sysbox?tab=readme-ov-file https://gvisor.dev https://github.com/containers/bubblewrap?tab=readme-ov-file
For hardware virtualized machines it much harder but you can do it via: https://github.com/firecracker-microvm/firecracker/ https://github.com/cloud-hypervisor/cloud-hypervisor
Freestyle/other providers will likely provide better debugging experience but thats something you can probably get past for a lot of workloads.
The time when you/anyone should think about Freestyle/anyone is when the load spikes/the need to create hundreds of VMs in short spikes shows up, or when you're looking for some of the more complex feature sets any given provider has built out (forks, GPUs, network boundaries, etc).
I also highly recommend self hosting anything you do outside of your normal VPC. Sandboxes are the biggest possible attack surface and it is a feature of us that we're not in your cloud; If we mess up security your app is still fine.
https://GitHub.com/jgbrwn/vibebin
Also I'm a huge proponent of exe.dev
Obviously your service/approach is different than exe, more like sprites but like you said more targeted/opinionated to AI coding/sandboxing tasks it looks like. Interesting space for sure!
Still WIP, but the core works — three rootfs tiers (minimal Ubuntu, headless Chromium with CDP, Docker-in-VM), OCI image support (pull any Docker image), automatic thermal management (idle VMs pause then snapshot to disk, wake transparently on next API call), per-user bridge networking with L2 isolation, named checkpoints, persistent volumes, and preview URLs with auto-wake.
Fair warning: the website is too technical and the docs are mostly AI-generated, both being actively reworked. But I've been running it daily on a Hetzner server for my AI agents' browser automation, and deploy previews.
I'd love any feedback if you want to go ahead and try it yourself