Would be pretty magical if when you need a sandbox, you just SSH into it and it's already there, right? exe.dev popularized this UX, but I self-host a lot of things already, so I wanted something similar, but on my own server, which has plenty of spare RAM and CPU cores.
I tasked Gemini DeepResearch with finding what I can use to glue together something like exe.dev. In a typical Gemini Deep Research fashion, it came back with a very obscure recommendation claiming everyone is using it. Repository had one fork and six stars at the time of search.
While obscure, Gemini IMO found a gem: https://github.com/kkovacs/vmtree
It's a collection of a few short bash scripts which automatically provision sandboxes using ssh as a trigger. It has other nice touches such as: controlling how sandboxes get cleaned up, and provisioning subdomains with or without HTTP authentication to expose services running inside the sandbox.
I love it. Mine is deployed entirely inside the VM (HTTPS and SSH DNAT'ed), and doesn't interfere with other VMs on my server.