Project Now

Just released by a London-based team, this app claims to "play the perfect music for every situation you are in", based on factors including your motion and geographical position, the time of day/week, weather, the volume of the surrounding area, and even the "lunar cycle". So, you'll get happier music on sunnier days, faster tunes when you're in a rush, and commute-friendly "walking music until you arrive at work then it automatically switches to your office music" -- which'll be sad songs because it's sunny outside.