If you feel like doodling with Docker on your Raspberry Pi, get thee to the home of Hypriot OS, a Debian derivative designed to run Docker on the famous single-board computer.
The 232MB download requires just 600MB of disk space when running, runs Engine Docker 1.12.1 and supports cluster mode. The latter is important: containers are designed to run across clustered kit, so the chance to do it on cheap rPis means an opportunity to mess around with containers at scale.