How is "lxd" different from lxc/docker?

Questions

• How does lxd provide Full operating system functionality within containers, not just single processes?
• How is it different from lxc/docker + wrappers?
• Is it similar to a container that is launched with docker + supervisor/wrapper script to contain multiple processes in one container?

In other words:

• What can I do with lxd that I cannot do with some wrappers over lxc and docker ?
• Why is it available only in ubuntu if they are making use of mainline kernel features (namespaces and cgroup )?

LXD works in conjunction with LXC and is not designed to replace or supplant LXC. Instead, it’s intended to make LXC-based containers easier to use through the addition of a back-end daemon supporting a REST API and a straightforward CLI client that works with both the local daemon and remote daemons via the REST API.

LXD is more like docker host.