Docker uses resource isolation features of the Linux kernel such as cgroups and kernel namespaces to allow independent "containers" to run within a single Linux instance, avoiding the overhead of starting virtual machines.
The technology of containers is not new, Solaris had this 10 years ago, but it is now free and easy.
After two years of gathering hype and bringing attention to long-neglected Linux containers, Docker announced ... that it will offer Docker Hub Enterprise, its first commercial product offering, in February of 2015. Docker Hub Enterprise is an on-site version of the company’s popular online repository for Docker images.
Getting Started with Docker @ CoreOS
Docker containers can boot extremely fast (in milliseconds!) which gives you unprecedented flexibility in managing load across your cluster.
How To Set Up a Private Docker Registry on Ubuntu 14.04 | DigitalOcean