See also: Hash
Home Page: http://bitzi.com
A metadata system revolves around a file's BitPrint (unique hash). Bitzi stores the bitprint and some attributes about the file. One of the possible uses of Bitzi is to discover if a file on a P2P system is a Cuckoo's Egg. Since the Bitzi catalog is searchable, it can also be used to find hash-links.
Bitzi is a community maintained database similar to the CD database FreeDB. Its contents are freely distributable under the OpenBits license, but the only full data dump is over 2 years old.
Bitzi support is directly built into several file sharing clients, including LimeWire, BearShare, Shareaza, and Gtk-Gnutella.