Zeitgeist is an "Event Logging Framework" that provides cross
application awareness of the desktop's activities.

You worked on a file, but you cannot remember where you saved it? You
visited a web page about basketball three days ago, but you cannot
find the URL in your browser's history? No problem, this is where
Zeitgeist enters the scene. It knows a lot about your activities and
has a feature rich D-Bus API which allows GUI applications like
gnome-zeitgeist, zeitgeistfs and others to present you your
activities in a readable way.