Think about this: Wouldn't it be nice if installing apps on your desktop was as simple as just a folder? And everything lived in that folder instead of sprawling out into the OS everywhere? Copy that folder to run more, or replace it to update, or delete it to remove everything.

That's what Docker does. It lets you wraps everything into a single isolated package (a container) that can run whatever you want without affecting anything else on the system, and then cleans up perfectly. You can connect it to networks and disks but There were APIs for most of these things already in Linux but Docker brought it all together into a simple interface.

The other big innovation is the Docker registry that makes images easily available over HTTP. No more complicated downloads or package systems, instead you could just point to a simple host/image:label address and download whatever you need. That simplicity and flexibility is what made it take off.