Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Walling for Windows - Visual walls for your ideas and projects. Now on Windows.
Asana Boards - A simple, visual way to track your team’s work
Milanote - Milanote is a note taking app for creative work.
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.
Four note boards - A simply stupid text tool to help think multidimensionally