Haystack is a project at MIT, whose "goal is to make it easier for people to collect, organize, find, visualize, and share their information. One of the biggest obstacles to such information management is the rigid, centrally-planned information models and user interfaces of existing applications and web sites. The data people use in the real world is rarely so well-formed. It is full of exceptions and idiosyncrasies. Our group develops tools for the web and desktop that can flex to hold and present whatever information a user considers important, in whatever way the user considers most effective."
One of the applications that grew out of it is list.it, which works with Firefox. I referred to some of the research behind this application in an earlier post. See Information scraps. See also Why Computers Can't Kill Post-Its at Forbes.