It's probably also worth mentioning dokku, which is a simplified private PaaS built on top of Docker. It adds Heroku buildpacks (Ruby, NodeJS and Java right now

It's probably also worth mentioning dokku, which is a simplified private PaaS built on top of Docker. It adds Heroku buildpacks (Ruby, NodeJS and Java right now) into the mix, and a git push-to-deploy model. Because dokku has a concise and readable codebase, browsing the source is a good way to see one practical application of Docker, too. I've set it up as a sandbox environment for developers at my company, and for our purposes it's a much better fit than some of the more heavyweight private PaaS products. I'm really enjoying working with it!