Probably your best option is a kiosk desktop since it would use a public login account. That will allow you to display the calendar without having a full user system, and no regular user login. This is what we did for the state prisons for inmates to use for specific tasks and then it can be in-depth controlled so they cannot do anything they shouldn't be doing.
A tablet could probably do what you want as well. If my memory serves me right, I remember seeing a tablet in a company or hospital to display exactly what you're looking to do.