What is the container for / what does this do that `docker save some:img | ssh wherever docker load` doesn't? More efficient handling of layers or something?

Yeah exactly, which is crucial for large images if you change only a few last layers.

The unregistry container provides a standard registry API you can pull images from as well. This could be useful in a cluster environment where you upload an image over ssh to one node and then pull it from there to other nodes.

This is what I’m planning to implement for Uncloud. Unregistry is so lightweight so we can embed it in every machine daemon. This will allow machines in the cluster to pull images from each other.

Relatively early on the page it says:

"docker save | ssh | docker load transfers the entire image, even if 90% already exists on the server"