> One feature driving Docker adoption that I think a lot of people miss is that it's got fairly workable (if warty in one case and obnoxious in the other) implementations for OS X and Windows. That removes a lot of friction for developers who work in companies where IT won't support Linux on employee workstations.
Vagrant does this, too. Sure, it runs a VM, but so does Docker.
Inside of Linux, yes Docker does utilize cgroups, namespaces and some other stuff for isolation. However, the GP is almost certainly talking about "Docker for Windows" and "Docker for OS X", which do not run directly on the host OS, and need to be run inside of Linux VMs (like Vagrant).
Well, there is a big difference, but not the one you've managed to come up with. Vagrant is normally used to run full VMs (although you can use it to drive Docker), so while you might run App, Supporting App, PHP, Apache, Node, Nginx, MySQL, Mongodb, and Redis all as separate containers, you'd probably put them all on the same VM. Your comment almost makes it sound like you don't understand Vagrant or VMs.
Vagrant does this, too. Sure, it runs a VM, but so does Docker.