Docker-machine drivers can be added into Rancher so that they can be available to add hosts into Rancher. Only an admin can change which machine drivers are visible, which can be located in Admin -> Machine Drivers.
The active machine drivers are the only options that are displayed on the Infrastructure -> Add Hosts page. By default, Rancher provides many machine-drivers, which only a subset are Active in our UI.
You can easily add your own machine-driver by clicking on Add Machine Driver.
After clicking on create, Rancher adds the additional driver and will display this option in the Driver field of adding other hosts or with a custom image (if provided).