Jamocracy (the name is a pun for Jam and Democracy) is exactly that: A democratic voting system for Partys. Users can add tracks and vote on them. The party owner can adjust various settings, allowing for a very much personalized experience.
Juky is an app which allows everyone to be the DJ of your party. Juky allows all guests to suggest and vote for Spotify songs they would like to hear. The song with the most votes will be played, so there will always be a song playing that most people like.