All this innovation in Docker is possible because the projects rely on a very broad community. Docker is a very intense and active project, split into several Github repositories, the most notable of which are:
Docker itself, the engine: www.github.com/docker/docker
Machine, the Docker hosts instantiator: www.github.com/docker/machine
Swarm, the orchestration service: www.github.com/docker/swarmkit
Compose, the tool to model micro services: www.github.com/docker/compose
Infrakit, the infrastructure manager: www.github.com/docker/infrakit
But also, these projects would not run without their libraries, such as Libcontainer, Libnetwork, Libcompose (waiting to be merged with Compose), and many many others.
All this code would not exist without the commitment of the Docker team and the Docker community.
Any company or individual is encouraged to contribute to the projects. There are some guidelines at https://github.com/docker/docker/blob/master/CONTRIBUTING.md.