Hey there c0fe –
openshift and tectonic have intersections with Juju, but are focused exclusively on Kubernetes.
Juju is an application modeling framework, much as those technologies are, but the interesting bit is it allows you to deploy anywhere you would like, from bare metal to the cloud. It’s not currently focused on immutable containers, but rather on more traditional applications.
For instance, the way you would deploy an openstack cluster, or a k8s cluster.
This space is indeed one with many technologies that all have bits and pieces of each other, so I don’t blame you for being confused.