Pandora, a free service, assembles personalized radio stations based on your tastes, but does it in a whole new way. Rather that relying on music that other people like, it relies on the innate quality of the music that you like, and finds more music like it. It grew out of something called the Music Genome Project (http://pandora.com/mgp.shtml) in which musicians went in and classified all kinds of characteristics of music, “everything from melody, harmony and rhythm, to instrumentation, orchestration, arrangement, lyrics, and of course the rich world of singing and vocal harmony.” Songs play instantly through the browser with an elegant, easy to navigate interface.

Field test: I tell Pandora I like the Replacements. It immediately plays a song called “Lie Down and Die” by Dag Nasty (never heard of Dag Nasty before). Why? That song, like the work of The Replacements, has “punk roots, repetitive melodic phrasing, mixed acoustic and electric instrumentation, major key tonality, and a gravelly male vocalist.” Awesome.

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