There is no mention on LXC/jails which is ofcourse the biggest inspiration for docker, if I am not mistaken it also used lxc under the hood. That was already a good'ish product and but hard to configure and not for the mainstream at the time. Docker introduced AUFS and downloading of images which was added. I always saw docker as a properly marketed nicely ribboned lxc but mediocre implemented since they removed a lot of options at that time that were super useful like cpu limiting etc from std lxc.