Spotify

A few years back some far-sighted people were envisioning "The Celestial Jukebox": the possibility of letting people play any music they wanted, on any device they wanted, in any place and at any time they wanted. "The killer app for music."

But there were substantial technical, legal, and economic obstacles to overcome.

Now, Spotify seems to be close to it: "The World's Greatest Music Service" (Slate, 7/16) and "Spotify Is the Best Desktop Music Player We've Ever Heard" (Lifehacker, 8/6). One remaining catch is that it's not yet available in the U.S.

But they're supposedly working on it.