The free site, started by former MTV marketing executive David Hyman with $1.4 million from private investors, requires users to download its application, MOG-O-MATIC.
The application catalogs the music on users' computer hard drives andand what new tunes are added through online downloads and portable music players.
The data is analyzed several ways and posted to users' MOG Web pages, which are open to inspection by the online world at large. Users also are encouraged to create their own blogs on their pages about their musical favorites.
"There are music lovers who want nothing more than to tell the world what they are listening to," MOG.com spokeswoman Dana Smith said. "This is really exciting to people who want to see what other people are listening to and to people who want to show off their stuff."
The company does not generate music recommendations from the data but does provide 30-second sound links to all users' collections as well as links to Apple Computer's iTunes Music Store and music e-tailer Amazon.com.