http://inbflat.net/

これは不思議な面白さ。YouTubeの演奏ビデオをコラボする楽しさ。色々なパターンを試したくなる。

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.