I think the majority of comments have it right; Vagrant is another abstraction layer that can utilise Docker.  IMO Vagrant (with either VBox or AWS) is better suited for developers because Docker relies on the Linux Kernel.  So if you're on a Mac or a different flavor of Linux, or God forbid Windoz you're going to get dev/prod discrepancies.

Australia Post is Vagrant customer building VM images and running in AWS.

+Terrence Miao​, yeah, we just had Docker taken off our approved technologies list.

Why is that +Dean Budd? I do know of some valid security concerns with Docker that has some DevOps mates of mine refuse to use it in prod.

We're being taken over by people who know better.

The person/people who make these decisions asked me "What's Docker?"