this is awesome.
the infinite jukebox.

its created with the echo nest api.

from their faq:

How does it work? – We use the Echo Nest analyzer to break the song into beats. We play the song beat by beat, but at every beat there’s a chance that we will jump to a different part of song that happens to sound very similar to the current beat. For beat similarity we look at pitch, timbre, loudness, duration and the position of the beat within a bar. There’s a nifty visualization that shows all the possible transitions that can occur at any beat.

Are there any ways to control the song? Yes – here are some keys:
[space] – Start and stop playing the song
[left arrow] – Decrement the current play velocity by one
[right arrow] – Increment the current play velocity by one
[Down arrow] – Sets the current play velocity to zero
[control] – freeze on the current beat
[shift] – bounce between the current beat and all of the similar sounding beats. These are the branch points.
‘h’ – Bring it on home – toggles infinite mode off/on.