I previously did not use our app frequently as it only played one song and there was no play button. It plays audio in sync on multiple devices via the web and prior it did so without a play button.

Though after being on stage at a DC Tech event and hearing the organizer complain to the audience of the UX we added a play button & ability to play a bunch of songs. We now use it everyday and more people are too.

http://speakerblast.com (if interested)