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.
J. Tang, J. Zhang, L. Yao, J. Li, L. Zhang, and Z. Su. Proceedings of the 14th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, page 990--998. New York, NY, USA, ACM, (2008)
S. Ries, J. Kangasharju, and M. Mühlhäuser. On the Move to Meaningful Internet Systems 2006: OTM 2006 Workshops, volume 4277 of Lecture Notes in Computer Science, page 894--903. Berlin/Heidelberg, Springer, (2006)
S. Bloehdorn, O. Görlitz, S. Schenk, and M. Völkel. Proceedings of the 6th International Conference on Knowledge Management (I-KNOW 06), Graz, Austria, (September 2006)
S. Ferré, and O. Ridoux. Proceedings of the 9th International Conference on Conceptual Structures, volume 2120 of Lecture Notes in Artificial Intelligence, page 187-201. Springer, (2001)