Earth allows you to find files across a large network of machines and track disk usage in real time. It consists of a daemon that indexes filesystems in real time and reports all the changes back to a central database. This can then be queried through a simple, yet powerful, web interface. Think of it like Spotlight or Beagle but operating system independent with a central database for multiple machines with a web application that allows novel ways of exploring your data.
D. Gifford, P. Jouvelot, M. Sheldon, and J. O'Toole. Proceedings of the 13th ACM Symposium on Operating Systems Principles, 25, page 16-25. Pacific Grove, California, United States, ACM Press, (1991)