Described at
https://github.com/dotcloud/docker/tree/v0.7.0, "Docker is an open source project to pack, ship and run any application as a lightweight container
Docker containers are both hardware-agnostic and platform-agnostic. This means that they can run anywhere, from your laptop to the largest EC2 compute instance and everything in between - and they don't require that you use a particular language, framework or packaging system. That makes them great building blocks for deploying and scaling web apps, databases and backend services without depending on a particular stack or provider.
Docker is an open-source implementation of the deployment engine which powers dotCloud, a popular Platform-as-a-Service. It benefits directly from the experience accumulated over several years of large-scale operation and support of hundreds of thousands of applications and databases."
Might be interesting, but like many other projects, they seem to be incapable of expressing concepts in basic English, e.g. who needs it, what does it do, etc.