YouTube as multi-channel musical mixer: http://inbflat.net/

Inbflat_net

I love this: saw it a couple of months ago but forgot to post it.

play these together, some or all, start them at any time, in any order. 

In Bb 2.0 is a collaborative music and spoken word project conceived by Darren Solomon from Science for Girls, and developed with contributions from users.

The videos can be played simultaneously -- the soundtracks will work together, and the mix can be adjusted with the individual volume sliders.

http://inbflat.net/