DockerUI - Created by Michael Crosby, later handed off to me when he got busy at Docker. The goal was to provide parity with the Docker command line, no extra features.
UI for Docker - Rename of the same project due to trademark concerns
Portainer - Fork of the original codebase with an expanded feature scope. I started losing interest in keeping up with Docker features when they added native Swarm, combined with a job change it was a good time to hand off the torch to someone else. It looks like they're trying to make a company out of it, I'm interested to see if they can make it happen.