Festify Gives Party Guests the Option to Vote for the Next Spotify Song
Windows / Mac: Making a party playlist is a bit of a tricky task. If you don’t trust your ability to do it yourself, Festify lets you create a playlist and then ask your friends to vote for songs next.
By creating your playlist with Festify, you invite your friends to the list and they can vote on tracks from their mobile devices. Any track with the most votes is played next. The app is still in beta testing but still works pretty well. You need a Spotify Premium account to use Festify.
Festify (free)