
Gnutellafan said many right thing about gnutella and magnet link, but he miss a few of fundamental points.
1) The Magnet link technology is from
Bitzi.
That site mantain a database of metadata (data about data) of files.
Go there and see and use the search engine.

2) The Magnet link technology use the SHA1 hash to identify a file (hashes are numbers that identify in a unique way a file). The SHA1 hash is very strong and can not be forged (so no one can take a SHA1 hash and build a file with the corresponding hash).
3) Bitzi NOW distribute a little program called "Bitcollider" that do the SHA1 and TigerTree (explaining later) hashes and extract metadata about a file (e.g. the ID3 tag in MP3, etc.) and submit them to Bitzi (or print them for you). Also it compute the edonkey hash and the fasttrack hash.
So if you go to Bitzi, you can obtain the link to a file in FastTrak, Edonkey and Gnutella.
4) The TigerTree hash is there for a good purpose.
The TigerTree specification enable to create a "tree of hashes" so when you download a file you must not wait the end of the download to kwon if the file is corrupted or not. You (your program) can check every chunk of the file was downloaded and verify it.
So a third party can not "poison" a file during a multiple download.
So if there is a release of a DVD or CD for X-box it can be searched and finded in all the three networks