I am looking for a project management tool. Ideally, it would be based on a flow chart thing, like a web site map. For each element in the flow chart, you should be able to make notes, assign tasks etc, and then link other elements. So if would be like Trello, if the Trello cards could have children/parent relationships. The closest thing I found is feature map.co. Any suggestions? It needs to be free like trello, or at least affordable with a free trial.