Docker was first released in March 2013. The initial commit of docker consisted of a light wrapper written in the Go language to set up, manage, and execute LXC containers in Linux.

Docker is now an open platform for developing, shipping, and running applications. It allows you to build, run, test, and deploy distributed applications inside software containers.

Docker provides an additional layer of abstraction and automation on OS-level virtualization in Linux, and now, on Windows as well. It uses the resource isolation features of the Linux kernel cgroups and namespaces, and a union-capable file system, UnionFS (for example: AUFS, btrfs, vfs, and DeviceMapper).

Docker now includes its own libcontainer library to use the virtualization facilities from the Linux kernel in addition to using abstracted virtualization interfaces via libvirt, LXC, and systemd-nspawn.

From the Docker website - Docker provides tooling and a platform to manage the lifecycle of your containers:

• Encapsulate your applications (and supporting components) into Docker containers
• Distribute and ship those containers to your teams for further development and testing
• Deploy those applications to your production environment, whether it is in a local data center or the Cloud