About: I love brainstorming, which ever topic, let it some tech inside, I'm available for a limited time but I appreciate
I will try to give a simple explanation. I am not expert with these technologies.
Maybe you tried to write "Kubernetes", it's equal to "Composer" for PHP, Kubernetes run with Docker; and you have a great production of containers.
The software for Virtual Machines runs on a separate guest OS, and Docker run the images within the same OS Kernel. (other important difference it's Hypervisor vs Kernel)
I don't know Rancher and Boxes.
My english is bad :P
Long in short:
Wikipedia is a great resource.