I've worked on the Rails backend for this as a freelancer. Moodelizer is a pretty cool solution if you have any kind of video or film, and easily want to add dynamic high-quality, music to it. Thanks to a built-from-scratch time stretch algorithm, you can set the music exactly on beat to where your cuts in the video are placed. Moodelizer should especially be interesting for any startup who are producing promotional films or screencasts for their product.