Treedolist

Treedolist is a hierarchical system for organising personal information. You can store tasks, lists, weblinks, notes, RSS feeds and more. You can manipulate your tree in a simple, intuitive interface with drag-and-drop or keyboard shortcuts. You can categorise items in your tree by due date or urgency. You can share single items or whole branches of your tree with your friends.

http://treedolist.com/