Maybe I am a bit naive, but in my mind it's just a simple software running between the OS and the tool in question which runs said software in some kind of virt

Maybe I am a bit naive, but in my mind it's just a simple software running between the OS and the tool in question which runs said software in some kind of virtualization, passing all requests to the OS after a check what they might want to do. I know that's what said tools are offering, but installing (and running) docker on Windows feels like loading up a whole other OS insides OS, so that even VM (Software) looks lean compared to that! But I admit, that I have no real experience with docker and the like.