qemu-docker is a base Docker container containing KVM-enabled qemu binaries, and scripts to set up the /dev/kvm device node (which udev would normally do for us in a non-containerized environment). It is meant to be built on top of using FROM in another Dockerfile (it's kevin/qemu in the Docker index).
Must be run with -privileged in order to take advantage of KVM, until the /dev/kvm device node is whitelisted for use within containers. If run non-privileged, qemu will fall back on software emulation.