Trello is the free, flexible, and visual way to organize anything with anyone.
Drop the lengthy email threads, out-of-date spreadsheets, no-longer-so-sticky notes, and clunky software for managing your projects. Trello lets you see everything about your project in a single glance.
A. Butz, T. Höllerer, S. Feiner, B. MacIntyre, and C. Beshers. Proceedings of the 2nd IEEE and ACM International Workshop on Augmented Reality, page 35--. Washington, DC, USA, IEEE Computer Society, (1999)