Docker Engine native install only on Ubuntu or other Linux distros?

I’m new to Docker so still trying to understand it. I Install it on Ubuntu 14.04, ran through some examples you had no problem. Now I’m trying to understand the overall concepts and where and when and how it runs. Trying to figure out how to apply it in our work and what might be its issues and limitations.

So I was a little confused and was not sure as I saw this "Docker Engine or “Docker” creates and runs Docker containers. Install Docker on Ubuntu, Mac OS X, or Windows. Or use the Install menu to choose from others. “As I thought it ran un a variety of Linux distro’s. But this states Ubuntu on this Docker page. But looking further maybe only the Docker Engine has to ultimately be on Linux? Docker Machines can be on other distros?

Documentation was clear that windows and MAC OS X cannot run natively.