Earlier quoted context omitted.
SwarmKit and ClassicSwarm are not "docker swarm", but AFAIK precursors of it until they've been merged into Docker itself. As a production user of Docker Swarm though, it is effectively dead and I've been planning a migration to k8s ASAP.
Swarmkit is the code that runs "Docker Swarm", it is vendored in to build it. I don't think anyone really uses Classic Swarm any more, and it was a precursor.
I stand corrected, thanks.