Pandora is a different kind of streaming music radio station. Unlike other services that offer recommendations based on similar purchases made by other users, Pandora uses the idea of a Music Genome to tag songs into distinct categories:

We ended up assembling literally hundreds of musical attributes or “genes” into a very large Music Genome. Taken together these genes capture the unique and magical musical identity of a song - everything from melody, harmony and rhythm, to instrumentation, orchestration, arrangement, lyrics, and of course the rich world of singing and vocal harmony.

An article on the Wall Street Journal on Unraveling Music’s DNA has more details:

Visitors to Pandora’s Web site are greeted with an invitation to enter the names of a few songs or artists they like. Pandora then generates a customized “radio station” that plays other songs it believes users will like, based on its scientific analysis. Users can click a tab to find out why Pandora has recommended a particular song — in the case of the Pink Floyd tune, Pandora says it is similar to “Come Together” in that it has “mild rhythmic syncopation, minor key tonality, repetitive melodic phrasing, extensive vamping and vocal harmonies.”

The interface is simple to use, with no additional software or plugin requirements other than Macromedia Flash. After some investigation, I discovered that the interface is actually built on the open source OpenLaszlo project, a platform that allows developers to create applications with the rich user interface capabilities of desktop client software and the instantaneous no-download Web deployment of HTML. The OpenLaszlo SDK consists of a compiler written in Java, a runtime JavaScript library, and an optional Java servlet that provides additional services to the running application.

An advertisement-supported version of Pandora is usable for free. A full, unlimited one-year subscription costs a mere price of $36 dollars a year. I’ve already paid for a one year subscription, so if you have any questions, feel free to ask.