As you can see from the homepage at http://rancher.com/, on the face of it, Rancher looks a lot like Portainer:

While it is true that both can be used to deploy and manage your containers, they inhabit two different spaces. The differences start with the installation process. Rancher does not currently support Docker for Mac or Docker for Windows. If you are using these platforms, you must use a local virtual machine running Ubuntu 16.04 or higher with a minimum of 1 GB of RAM. However, to take proper advantage of Rancher, I recommend that you use a server instance that is publicly accessible.