We use Screenly. It's rather basic and managed from a cloud account that can see the devices. There is no SSH or other "admin" access beyond the Web GUI that allows you to name/rename/remove and group screens based on their onsite locations for common signage. We've had issues with them and I'm looking for software to replace Screenly that will run on Raspbian or other Unix-like ARM OS.
Author of Screenly here. Please ping me on Twitter (@vpetersson) to see how we can help.
I'm working on this. I have a solution about ready to launch and I have a question for you. What do you wish it had SSH to do ? I decided not to include it for security, what is not available in the web gui that you would find useful ?