Indiloop

Indiloop has created the easiest way to remix music.
The drag & drop interface allows you to mix and match stems (isolated instrumental and vocal parts) from your favorite songs into the mixer then watch them snap together in the same BPM and Key. Pick up where you left off on any mobile device, laptop or desktop computer, share your remix to your social networks, and turn the music you like into the music you love.

Disclaimer:
All audio content is accessed via the cloud, so you must have a decent internet connection in order to use Indiloop.