Why do you need a "service" for this? It looks like something you could run very well locally.

You don't need it, it's essentially a hosted version of their tool bake[0], which is actually pretty slick - without any setup you can go from a system with just KVM to running any random docker container. I can think of a few use cases for this, especially anything where you want to use containers as the delivery mechanism

[0]: https://github.com/losfair/bake

I hope you have read the article. They literally say as the other commentor points, that they essentially use bake. You could rather host something like this pretty trivially I suppose.