Any Linux desktop user will have used KDE at some point. Currently, KDE is at version 3.something, but there's already talk about what's going into KDE 4. Perhaps the most interesting addition is the new linking and searching facility.
One prominent effort in Appeal is Tenor, a "contextual linkage engine." Tenor will gather contextual data -- such as the metadata stored in MP3s, the contents of text files, and relationships between a file and the application that created it -- and present it to applications via another KDE framework. This will allow applications to provide more useful ways of searching files for users. For example, using Tenor an application could bring up a list of "all the images I downloaded from the Web in the past week."
Sounds a little WinFS-esqe to me. Newsforge has the full story.