Assembla Introducing Simple Planner for lightweight Agile, Scrum, and Kanban
blog.assembla.com
blog.assembla.com
I am not saying that planning tools can't be innovative but most of them are a combination of overly complex and not easy on the eyes.
I am assuming that most people who want to go with a scrum board that is digital are going to use trello https://trello.com/. I again believe even trello is overly complex but at least it's easy to look at.
I love Trello, but it's supposed to be generic, and thus, not easy to use it as a Kanban board (limit number of cards per list, etc) out of the box.