Based on my previous Force.com app for managing Salesforce Cases on a Kanban board, I've built Kanban for Salesforce, a project management tool on the Force.com platform. It uses a custom object for cards so it's not tied to an existing Salesforce native object. Cards can be organizated into sprints.
The state is that great fiction by which everyone tries to live at the expense of everyone else. - Frederic Bastiat